Irregular plural nouns list with definitions and examples

1. Irregular plural nouns list with definitions and example sentences

Below is an A–Z list of irregular plural nouns in English that you may not be aware of. I have included clear definitions and example sentences to help you use them correctly. Blue shows the singular form; green shows the plural form.

a vehicle that can fly, such as an aeroplane or helicopter

The military aircraft landed safely at the base after completing its reconnaissance mission.

During World War II, over 300,000 aircraft were produced by American factories alone.

a former student or graduate of a particular school, college, or university

Barack Obama is a famous alumnus of Harvard Law School, where he served as president of the Harvard Law Review.

The university's alumni donated over $50 million to fund new research facilities last year.

a detailed examination of something to understand its nature or determine its essential features

The detective's analysis of the crime scene revealed crucial evidence that had been overlooked.

Financial analyses conducted by major banks predicted a market correction before the 2008 crash.

supplementary material at the end of a book or document; also a small organ attached to the large intestine

The research paper included three appendices containing raw data and statistical calculations.

Surgeons at major hospitals perform hundreds of emergency appendix removals each year when appendices become inflamed.

an imaginary line around which something rotates; a fixed reference line for measuring coordinates

The Earth's axis is tilted at approximately 23.5 degrees, which causes our seasons.

When graphing equations, mathematicians plot points along both the x and y axes.

a microscopic single-celled organism that can cause disease or perform beneficial functions

The bacterium E. coli was first discovered by German paediatrician Theodor Escherich in 1885.

Billions of helpful bacteria live in the human gut and aid in digestion.

a large wild ox with a shaggy mane, native to North America and Europe

Yellowstone National Park is home to the largest free-roaming bison herd in the United States.

Conservation efforts have increased the North American bison population from fewer than 1,000 in 1900 to over 500,000 today.

a large bovine animal found in Africa and Asia; also refers to the American bison informally

The water buffalo remains essential to rice farming across Southeast Asia.

Native American tribes relied on buffalo for food, clothing, and shelter for thousands of years.

a succulent plant with thick stems and spines, typically found in desert regions

The saguaro cactus can live for over 200 years in the Arizona desert.

Botanical gardens in London display rare cacti from every continent except Antarctica.

a young cow or bull; also the fleshy back part of the leg below the knee

The farmer watched as the newborn calf took its first wobbly steps.

Marathon runners often experience painful cramps in their calves during the final miles of a race.

a young human being below the age of puberty or legal majority

UNICEF estimates that one child dies every few seconds from hunger-related causes worldwide.

The children at the orphanage received new books donated by the local library.

a time of intense difficulty, danger, or uncertainty requiring immediate action

The 2008 financial crisis led to the collapse of Lehman Brothers and worldwide economic turmoil.

Climate scientists warn that multiple environmental crises are converging simultaneously.

a standard or principle by which something is judged or decided

The Nobel Prize committee uses scientific impact as the primary criterion for selecting laureates.

UFC fighters must meet strict weight criteria before being allowed to compete in their division.

the subjects and content taught in a school or educational program

Finland's innovative curriculum emphasises creativity and critical thinking over standardised testing.

Many universities are updating their curricula to include courses on artificial intelligence and data science.

a single piece of information or fact used as a basis for reasoning or calculation

Each datum collected from the Mars rover helps scientists understand the planet's geology.

Tech companies like Google and Meta collect massive amounts of user data every second.

a hoofed grazing animal with antlers, found in forests and grasslands worldwide

A lone deer emerged from the forest at dawn, cautiously approaching the meadow.

Over 30 million deer live in the United States, causing thousands of vehicle collisions annually.

the identification of a disease or problem through examination of symptoms

The doctor's diagnosis confirmed that the patient had early-stage diabetes.

AI systems can now make accurate medical diagnoses faster than many human specialists.

a small cube with numbered faces used in games of chance

Rolling a single dice gives you a one-in-six chance of landing on any number.

Professional gamblers in Las Vegas study the physics of how dice tumble across the table.

a mythical small humanlike creature; also a person of unusually short stature

J.R.R. Tolkien popularised the spelling "dwarves" for the dwarf characters in his Middle-earth novels.

The seven dwarves in Disney's Snow White became some of the most beloved animated characters in film history.

a sound that is reflected off a surface and heard again; a repetition or imitation

The canyon walls produced a stunning echo that lasted several seconds.

Dolphins use echoes from their clicks to locate prey in murky waters through echolocation.

a supernatural being in folklore, typically depicted as small and mischievous

Legolas the elf became one of the most popular characters in Peter Jackson's Lord of the Rings trilogy.

Nordic mythology describes elves as powerful beings who could bring either fortune or misfortune to humans.

a cold-blooded aquatic vertebrate with gills and fins

The Atlantic bluefin tuna is one of the most valuable fish in the world, with specimens selling for millions.

Marine biologists have identified over 34,000 different fish species inhabiting Earth's oceans and freshwater systems.

the center of interest or activity; a state of clear vision or concentration

The photographer adjusted the focus until the distant mountain peaks became crystal clear.

NASA's current foci include returning humans to the Moon and eventually sending astronauts to Mars.

the lower extremity of the leg below the ankle; also a unit of measurement equal to 12 inches

Usain Bolt's foot speed allowed him to become the fastest human ever recorded.

Mount Everest rises 29,032 feet above sea level, making it Earth's highest peak.

a spore-producing organism that feeds on organic matter, including mushrooms, moulds, and yeasts

The fungus Penicillium notatum led Alexander Fleming to discover penicillin in 1928.

Scientists estimate that fungi decompose approximately 85% of all dead plant material on Earth.

a large waterbird with a long neck, related to ducks and swans

A Canada goose can fly at speeds exceeding 40 miles per hour during migration.

Thousands of geese gather at wildlife refuges along the Mississippi Flyway each autumn.

one of two equal parts of something

The referee blew the whistle to signal the end of the first half.

Tom Brady's legendary comeback saw the Patriots overcome a 25-point deficit across both halves of Super Bowl LI.

a person admired for courage, outstanding achievements, or noble qualities

Firefighters who rushed into the Twin Towers on 9/11 are remembered as true heroes worldwide.

Comic book heroes like Spider-Man and Batman have dominated box office revenues for over two decades.

the hard covering protecting the foot of a horse, cow, or similar animal

A farrier must trim and shoe a horse's hoof every six to eight weeks.

The thundering sound of hundreds of hooves echoed across the plains as the wild horses galloped past.

a proposed explanation for a phenomenon, used as a starting point for investigation

Einstein's hypothesis about the bending of light was confirmed during the 1919 solar eclipse.

Scientists at CERN test multiple hypotheses simultaneously using the Large Hadron Collider.

an alphabetical list of topics with page references; also a statistical measure of change

The S&P 500 index tracks the performance of 500 large companies listed on American stock exchanges.

Librarians maintain detailed indexes to help researchers locate specific information quickly.

a cutting instrument with a sharp blade attached to a handle

A chef's knife is considered the most essential tool in any professional kitchen.

Swiss Army knives have been standard equipment for military forces in over 100 countries.

a flat green structure attached to a plant stem, responsible for photosynthesis

A single leaf from the Amazon rainforest can support an entire ecosystem of insects.

New England's brilliant autumn leaves attract millions of tourists during peak foliage season.

the condition that distinguishes living organisms from dead matter; also the period of existence

Nelson Mandela dedicated his life to ending apartheid in South Africa.

The earthquake claimed over 200,000 lives and left millions homeless across Haiti.

a shaped mass of baked bread

The bakery produces over 500 fresh loaf units before sunrise each morning.

During World War II, rationing limited families to just two loaves of bread per week.

a small parasitic insect that lives on the skin of mammals and birds

A single louse can lay up to 10 eggs per day on a human scalp.

Head lice affect an estimated 6 to 12 million children in the United States annually.

an adult male human being

Neil Armstrong became the first man to walk on the Moon on July 20, 1969.

The Tuskegee Airmen were African American men who became legendary fighter pilots during World War II.

a rectangular array of numbers or symbols; also an environment in which something develops

Computer graphics rely on matrix mathematics to render three-dimensional images.

Statisticians use correlation matrices to identify relationships between multiple variables.

a means of communication or expression; also a middle state between extremes

Television emerged as the dominant medium for news consumption throughout the late 20th century.

Social media platforms have transformed how politicians communicate with voters.

a written message in business or diplomacy, typically brief and informal

The leaked memorandum revealed secret negotiations between the two governments.

Corporate executives exchange thousands of memoranda daily regarding strategic decisions.

the largest member of the deer family, found in northern forests

A bull moose can weigh up to 1,500 pounds and stand over six feet tall at the shoulder.

Alaska's Denali National Park provides ideal habitat for moose, with an estimated population of 1,800.

a small rodent with a pointed snout and long tail; also a hand-operated computer device

Laboratory mice share approximately 85% of their genes with humans, making them valuable for research.

Before touchscreens became common, computer mice were essential for navigating graphical interfaces.

the central part of an atom or cell; also the core of something

The nucleus of an atom contains protons and neutrons bound together by the strong nuclear force.

Cancer occurs when cell nuclei begin dividing uncontrollably due to DNA mutations.

a fertile area in a desert where water is found; also a peaceful refuge

The Siwa Oasis in Egypt has supported human civilisation for over 10,000 years.

Ancient trade routes across the Sahara depended on oases spaced along the journey.

a domesticated bovine animal used for pulling heavy loads

Before tractors existed, farmers relied on a single ox to plough their fields.

Teams of oxen pulled covered wagons along the Oregon Trail during America's westward expansion.

a coin worth one cent in the US or one hundredth of a pound in Britain

Abraham Lincoln's profile has appeared on the American penny since 1909.

The price increased by fifty pence overnight, angering British consumers.

an individual human being

Elon Musk became the richest person on Earth in 2021, surpassing Jeff Bezos.

Over eight billion people now inhabit our planet, with the population still growing.

a fact or event that can be observed; something remarkable or extraordinary

The Northern Lights represent one of nature's most spectacular phenomena.

Scientists continue studying phenomena like dark matter and black holes to understand the universe.

an edible tuber native to South America, now a global food staple

The humble potato saved millions from starvation after Spanish explorers brought it to Europe.

Idaho produces approximately 13 billion pounds of potatoes annually.

a straight line from the centre to the circumference of a circle; also a bone in the forearm

The blast radius of the Hiroshima atomic bomb extended approximately one mile from the epicentre.

Astronomers calculate orbital radii to predict how planets move around their stars.

a large fish prized for its pink flesh, known for swimming upstream to spawn

Wild salmon can travel over 2,000 miles upstream to return to their birthplace for spawning.

Norwegian salmon farms produce over 1.5 million tons of salmon each year for global markets.

a length of fabric worn around the neck or head for warmth or fashion

Queen Elizabeth II was rarely seen without a silk scarf during public appearances.

Football fans wave colourful scarves to show support for their favourite teams.

a person's essential being that distinguishes them from others

Meditation helps people connect with their inner selves and reduce stress.

The survivors pushed themselves beyond their normal selves to escape the disaster.

a number of related events, objects, or broadcasts occurring in succession

Netflix's documentary series "Making a Murderer" sparked nationwide debate about criminal justice.

The World Series has determined baseball's champion team since 1903.

a domesticated ruminant mammal raised for wool, meat, and milk

New Zealand has approximately six sheep for every human resident.

Dolly the sheep became the first mammal cloned from an adult cell in 1996.

a flat horizontal surface for storing or displaying objects

The bookstore owner dusted each shelf before the morning rush began.

IKEA sells millions of Billy bookcases with shelves every year worldwide.

a small shellfish with a slender body, widely consumed as seafood

A mantis shrimp can punch with the force of a bullet, shattering aquarium glass.

Americans consume approximately 1.5 billion pounds of shrimp annually, making it their favourite seafood.

a vehicle designed for travel or operation in outer space

The Voyager 1 spacecraft has travelled farther from Earth than any human-made object.

SpaceX has launched more reusable spacecraft than any other company in history.

a group of organisms capable of interbreeding and producing fertile offspring

The giant panda is an endangered species with fewer than 2,000 individuals remaining in the wild.

Scientists discover approximately 18,000 new species every year, mostly insects and plants.

something that causes a response or reaction; also government spending to boost the economy

The COVID-19 stimulus package provided direct payments to millions of American households.

Neurons respond to external stimuli by sending electrical signals through the nervous system.

a layer of rock or soil; also a level or class in society

Geologists study each stratum of rock to understand Earth's geological history.

The Grand Canyon's colourful strata represent nearly two billion years of geological formation.

a pig or pigs collectively, especially when raised for food

China produces more swine than any other country, accounting for half of global pork consumption.

The H1N1 swine flu pandemic of 2009 infected an estimated 1.4 billion people worldwide.

a statement or theory put forward to be maintained or proved; also a long academic paper

Martin Luther's 95 thesis statements challenged the Catholic Church and sparked the Protestant Reformation.

Graduate students spend years researching and writing their doctoral theses.

a person who steals another person's property

The art thief managed to steal paintings worth over $500 million from the Boston museum.

Identity thieves compromise millions of personal records through data breaches each year.

a red or yellow fruit eaten as a vegetable, native to South America

The tomato was once believed to be poisonous by Europeans, who called it "the devil's fruit."

Italy produces over 5 million tons of tomatoes annually for the pasta sauce and pizza industries.

a hard structure in the mouth used for biting and chewing food

A great white shark can lose and regrow over 20,000 tooth structures during its lifetime.

UFC fighter Mike Tyson famously bit Evander Holyfield's ear during their 1997 rematch.

a self-propelled underwater missile launched from a ship or submarine

The German U-boat launched a torpedo that sank the Lusitania in 1915, killing 1,198 passengers.

Modern nuclear submarines carry up to 24 torpedoes capable of destroying enemy vessels.

a freshwater fish related to salmon, popular among sport fishermen

Rainbow trout can live up to 11 years in the cold mountain streams of the Rocky Mountains.

Fly fishermen travel from around the world to catch wild trout in Montana's pristine rivers.

a constitutional right to reject a decision or proposal made by a lawmaking body

President Franklin D. Roosevelt issued more veto decisions than any other American president—635 in total.

Russia and China have used their UN Security Council vetoes to block numerous sanctions resolutions.

a spinning mass of fluid or air, such as a whirlpool or tornado

The polar vortex brought record-breaking cold temperatures to the American Midwest in 2019.

Jupiter's Great Red Spot is a massive vortex storm that has raged for over 400 years.

a level surface built along the shore where ships can dock to load and unload

San Francisco's Fisherman's Wharf attracts over 12 million visitors annually.

The historic wharves of Boston Harbour witnessed the famous Tea Party protest in 1773.

a married woman, especially in relation to her spouse

Michelle Obama served as the wife of the 44th President and became a bestselling author.

King Henry VIII had six wives, two of whom were executed at his command.

a wild carnivorous mammal that lives and hunts in packs

The grey wolf was reintroduced to Yellowstone National Park in 1995 after being absent for 70 years.

A pack of wolves can travel up to 30 miles in a single day while hunting.

an adult female human being

Kamala Harris became the first woman to serve as Vice President of the United States in 2021.

The suffragette movement fought for decades until women won the right to vote in 1920.

2. What are irregular plural nouns?

To make plurals in English, we normally add -s or -es at the end of the nouns. For example, the plural of cat is cats; the plural of bus is buses. However, many nouns in English do not follow these patterns. For example, the plural of tooth is teeth. They are called irregular plural nouns.

In this grammar lesson, I have compiled a comprehensive list of irregular plural nouns in English.

There are hundreds of irregular plural nouns in English. While there is no single rule that applies to all of them, many follow recognisable patterns that can help you learn them more efficiently.

3. Why do irregular plural nouns exist?

The irregularities in English plurals are not random accidents. They are remnants of historical linguistic evolution that stretch back over a thousand years.

Old English had a complex system of noun declensions borrowed from its Germanic roots. Different groups of nouns formed their plurals in different ways, similar to how modern German still uses multiple plural endings. Over time, as the language simplified, the -s plural became dominant, but some ancient forms stubbornly persisted.

Words like men, women, and children survived because they were so commonly used that speakers never forgot their original forms. Additionally, English absorbed words from Latin and Greek, and many of these retained their original plural patterns in academic and scientific contexts.

4. The most common patterns for irregular plurals

Many irregular plural nouns fall into recognisable categories. By learning these patterns, you can remember them easily.

4.1 Pattern 1: nouns ending in -f or -fe

Many English words that end in -f or -fe form their plurals by changing the f to a v and adding -es.

4.2 Pattern 2: words ending in -o

Words ending in -o typically form their plurals by adding -es rather than just -s.

The rule is fairly consistent for words of English origin. However, for words borrowed from other languages, particularly Italian, we usually dd -s instead.

4.3 Pattern 3: vowel changes

Some of the most distinctive irregular plurals in English are formed by changing the vowel sound inside the word. This is called ablaut or umlaut. It traces back to Proto-Germanic roots and represents one of the oldest patterns in the language.

The list below contains words that are among the most frequently used in everyday speech, so you probably already know most of them. The vowel shift typically involves changing oo to ee or a to e.

4.4 Substantial changes

For various historical reasons, some English words change dramatically when made plural. These transformations can seem almost random, but they reflect very old linguistic patterns that have survived through centuries of use.

You must memorise them, as they do not follow any predictable modern pattern. Fortunately, most of them are extremely common, so you will encounter them frequently.

The word children is particularly interesting from a linguistic perspective. It actually contains two plural markers: the -r from an older declension pattern and the -en from a weak noun plural ending. This double marking explains why it sounds so different from child.

4.5 No changes

Perhaps the most confusing irregular plurals are those that remain the same in both singular and plural forms. The list below contains these zero plurals, which includes common animals and everyday objects.

1. sheep
2. deer
3. fish
4. moose
5. swine
6. buffalo
7. shrimp
8. trout
9. salmon
10. bison
11. aircraft
12. spacecraft
13. watercraft
14. hovercraft
15. series
16. species
17. cod
18. pike
19. reindeer
20. offspring
21. means

5. Latin and greek plurals in English

English has borrowed extensively from Latin and Greek, especially in scientific, medical, and academic contexts. Many of these borrowed words retain their original plural forms, though some have also developed anglicised alternatives.

5.1 Words ending in -us

Latin words ending in -us typically form their plurals by changing -us to -i. This pattern is common in mathematics, science, and formal writing, though many of these words also have accepted anglicised forms using -es.

5.2 Words with -is at the end

Words ending in -is typically form their plurals by changing -is to -es. This pattern is very consistent and applies to many words used in academic and technical writing.

5.3 Nouns ending in -on

Greek words ending in -on typically change to -a in the plural. These words are common in scientific and philosophical contexts and should be learned as pairs.

5.4 Singular forms ending in -um

Latin words ending in -um typically form their plurals by changing -um to -a. Many of these plurals are so common that they are more familiar than their singular counterparts.

5.5 Singular forms ending in -ix or -ex

These Latin-origin words typically change their endings to -ices in formal contexts, though anglicised forms ending in -xes are also widely accepted in everyday usage.

If you are craving for some practice, check my exercises on singular and plural nouns.