Plural of Hippopotamus

by Craig Shrives

The Quick Answer

The plural of hippopotamus is hippopotamuses or hippopotami.

The Plural of Hippopotamus

The plural of hippopotamus is hippopotamuses or hippopotami.
  • Hippopotamuses live in groups of up to thirty. correct tick
  • Though they are bulky animals, hippopotami can gallop at 19 mph on land. correct tick
Even though the noun hippopotamus has a Greek root, it is often assigned the Latin plural hippopotami. So, the plural form hippopotami is technically an error. Nevertheless, the word hippopotami has become an acceptable plural for hippopotamus. (Of note, the word hippopotami is often used by pedants with a highbrow tone, believing it to be correct. It is therefore ironic that the term is based on an error. Hippopotami is also used by some as a joke plural.)

The plural hippopotamuses (which adheres to the standard rules for forming plurals) is more common than hippopotami.

The shortened version hippos is often used in informal writing to avoid to making a decision on hippopotamuses and hippopotami.

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The Standard Rules for Forming the Plurals

The table below shows the standard rules for forming the plurals of nouns in English.
Type Example of Type Forming the Plural Plural
Most Nouns lamp
add s lamps
Noun Ending s, sh, ch, x or z hippopotamus
add es hippopotamuses
Nouns ending [consonant] o hero
add either s or es
(There are no rules for this - you have to know.)
Nouns ending [vowel] o patio
add s patios
Nouns ending [consonant] y story
change the y to an i and add es stories
Nouns ending [vowel] y donkey
add s donkeys
Nouns ending f or fe dwarf
ves and/or s
(There are no rules - you have to know.)
hooves or hoofs
Exceptions man
some nouns undergo a vowel or letters change men
More exceptions salmon
some nouns do not change at all salmon
Foreign rulings hippopotamus
some nouns adopt foreign rulings hippopotami
Read more about English spelling rules.

Why Is There Confusion over the Plural of Hippopotamus?

Confusion arises over the plural of hippopotamus because the erroneously assigned Latin plural hippopotami grew in popularity, most probably because it sounds funny and clever. Nowadays, however, native English speakers are more drawn to hippopotamuses, which adheres to the standard ruling for forming plurals.

Hippopotamuses is the more common plural of the two. (See the difference in Google's Ngram Viewer.)

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