Do You Know the 35 Hardest Plurals in the English Language?

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Tooth

Teeth is the plural of tooth. We thought we'd start with something easy.

Syllabus

Syllabi is the plural of syllabus. A syllabus is an outline, usually of a course.

Diagnosis

Diagnoses is the plural of diagnosis. Similarly, analyses is the plural of analysis.

Person

People is the plural of person. What rule does this follow?!

Radius

Radii is the plural of radius. Well, that's not confusing at all.

Crisis

Crises is the plural of crisis. For many words that end in "us," change the "us" to an "i" to make it plural.

Index

Indices is the plural of index. Huh? This is just one of those you have to memorize.

Criterion

The plural of criterion is criteria. We think most people have more trouble with the singular form of this one.

Ox

The plural of ox is oxen. Does that mean that the plural of box is "boxen"? Sigh.

Schema

The plural of schema is schemata. A schema is a pattern or structure.

Tableau

The plural of tableau is tableaux. Similarly, the plural of chateau is chateaux.

Die

The plural of die is dice. This is another one where the singular form is more misunderstood than the plural form.

Memo

The plural of memo is memos. Hey wait ... aren't we supposed to add an "es" to words ending in "o"?

Mongoose

The plural of mongoose is mongooses. Wait, shouldn't it be mongeese?

Roof

The plural of roof is roofs. But if the plural of knife is knives, why isn't the plural of roof "rooves"? We're so confused!

Human

The plural of human is humans. But if the plural of woman is "women," and the plural of man is "men," then why isn't the plural of human "humen"?

Moose

The plural of moose is moose. Well, that's not confusing at all.

Potato

The plural of potato is potatoes. Similarly, the plural of tomato is tomatoes. But remember, never spell tomato "tomatoe." That's just wrong.

Aquarium

The plural of aquarium is aquaria. We had to double check this one.

Cod

The plural of cod is cod. Like deer and hair, cod is the same in both the singular and the plural forms.

Hippopotamus

The plural of hippopotamus is hippopotami. Similarly, the plural of rhinoceros is rhinoceri.

Hoax

The plural of hoax is hoaxes. Nope, that's not a hoax.

Axis

The plural of axis is axes. Yup, the plural of axis is the same as the plural of axe.

Species

The plural of species is species. In some, very rare, instances, the word "specie" is used as the singular form.

datum

The plural of datum is data. We know what data is, but who knew that the singular form was "datum"?

Millennium

The plural of millennium is millennia. Add an "l" and you're talking about a generation: millennial.

Census

The plural of census is censuses. No, it's not censai.

Stylus

The plural of stylus is styli. Sometimes the word "styluses" is used for the plural.

Phenomenon

The plural of phenomenon is phenomena. Similarly, the plural of automaton is "automata."

Cello

The plural of cello is celli. But why isn't it "celloes"?

Elf

The plural of elf is elves. Similarly, the plural of self is "selves."

Scissors

The plural of scissors is scissors. Similarly, the plural of shorts is shorts.

Cul-de-sac

The plural of cul-de-sac is culs-de-sac. Similarly, the plural of brother-in-law is brothers-in-law.

Passerby

The plural of passerby is passersby. We think that goes against the rules.

Kennedy

The plural of Kennedy is Kennedys. The rule "change the y to an i and add es" does not apply to proper nouns.

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About This Quiz

Are you a grammar expert? Does the misuse of plurals on the internet drive you nuts? If you think you know more than the average Joe about the plural forms of common, and some uncommon, words, take this quiz to prove your knowledge.

The easiest way to make a word plural is to add an "s." But that doesn't work for every word. Some other rules of plurals include adding an "es" to words that end in "x," "ch," "s,: or an "s-like" sound; add an "ies" and drop the "y" for a word that ends in "y;" and add a "ves" and drop the "f" or the "fe" for words that end in "f" or "fe." But some words don't play by the rules. For instance, if the plural forms of potato and tomato are tomatoes and potatoes, then why isn't the plural of the word memo "memoes" (it's memos)? And some words don't have plural forms at all. For instance, the plural of moose is moose, the plural of fish is fish, and the plural of deer is deer. If you're not confused, then this might just be the quiz for you.

Let's find out how much you really know about irregular plurals.

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