Irregular plural nouns

In English, there are hundreds of nouns that don’t follow the standard rules for pluralization. There are no easy ways to remember them, so they generally have to be memorized.

Some of the rarer irregular plurals are often misused, leading to the creation of variant forms, which usually encounter resistance at first but eventually make it into the language. For example, the plural of formula has traditionally been formulae, but formulas is now far more common, and few would call it incorrect.

Latinate plurals

Some nouns have retained their plural forms from Latin and other languages:

singular plural
addendum addenda
alga algae
alumnus alumni
amoeba amoebae
antenna antennae
bacterium bacteria
cactus cacti
curriculum curricula
datum data
fungus fungi
genus genera
larva larvae
memorandum memoranda
stimulus stimuli
syllabus syllabi
vertebra vertebrae

-o becoming –oes

Most nouns ending in –o are pluralized by adding an –s, but some take –es instead—for example:

singular plural
echo echoes
embargo embargoes
hero heroes
potato potatoes
tomato tomatoes
torpedo torpedoes
veto vetoes

Changing vowel sounds

Some nouns change their central vowel sounds when pluralized—for example:

singular plural
foot feet
goose geese
louse lice
man men
mouse mice
tooth teeth
woman women

-f becoming –ves

Some nouns ending in –f are pluralized by dropping the –f and adding –ves:

singular plural
calf calves
elf elves
half halves
hoof hooves
knife knives
leaf leaves
life lives
loaf loaves
self selves
shelf shelves
thief thieves
wife wives
wolf wolves

-is becoming –es

Some nouns ending in –is are pluralized by dropping the –is and adding –es:

singular plural
axis axes
analysis analyses
basis bases
crisis crises
diagnosis diagnoses
ellipsis ellipses
emphasis emphases
hypothesis hypotheses
neurosis neuroses
oasis oases
paralysis paralyses
parenthesis parentheses
thesis theses

-ix becoming –ices

Some nouns ending in –ix are pluralized by dropping the –ix and adding –ices:

singular plural
appendix appendices
index indices
matrix matrices

Unchanged plurals

A few nouns are unchanged in their plural forms:

singular plural
barracks barracks
deer deer
fish fish
gallows gallows
means means
offspring offspring
series series
sheep sheep
species species

16 thoughts on “Irregular plural nouns”

  1. I’ve graduated high school roughly 5 years ago and went to catholic school growing up, which was very strict about grammar/spelling. This page, and your site in general, is an amazing help to jog back memories about how certain endings change and which wording you’d correctly use to make a sentence proper. Thank you, this was very easy to comprehend! Keep up the great work, I’m glad to see the kids commenting here are actually gaining from this too! Truly wonderful.


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