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Grammar Monster

Plural of Platypus

The Quick Answer
The plural of platypus is platypuses.

The Plural of Platypus

The plural of platypus is platypuses.
  • Both male and female platypuses are born with ankle spurs, but only the male's spurs produce venom.
  • In captivity, platypuses have survived up to 17 years of age.
The noun platypus has a Greek root. The Greek plural for platypus is platypodes, but this plural is not used in English. The plural platypi is sometimes mistakenly used by people who believe that platypus has a Latin derivation, meaning its plural would be platypi (in the same way that fungus, cactus, and hippopotamus become fungi, cacti, and hippopotami).

The noun platypus adheres to the standard rules for forming the plurals of nouns in English (shown in the table below).

Type Example of Type Forming the Plural Plural
Most Nouns lamp
scythe
add s lamps
scythes
Noun Ending s, sh, ch, x or z platypus
dress
add es platypuses
dresses
Nouns ending [consonant] o hero
zero
tomato
add either s or es
(There are no rules for this - you have to know.)
heroes
zeros
tomatoes
Nouns ending [vowel] o patio
ratio
add s patios
ratios
Nouns ending [consonant] y story
penny
change the y to an i and add es stories
pennies
Nouns ending [vowel] y donkey
chimney
add s donkey
chimneys
Nouns ending f or fe dwarf
hoof
ves and/or s
(There are no rules - you have to know.)
dwarfs
hooves or hoofs
Exceptions man
louse
some nouns undergo a vowel or letters change men
lice
More exceptions salmon
sheep
some nouns do not change at all salmon
sheep
Foreign rulings cactus
medium
some nouns adopt foreign rulings cacti
media

Why Is There Confusion over the Plural of Platypus?

Confusion arises over the plural of platypus because many believe it is a Latin noun that should be pluralized with an i (just like cactus becomes cacti).

Through common usage (even though incorrect), platypi is becoming an accepted plural for platypus. Nevertheless, the safest version to use is platypuses. (See the difference in Google's Ngram Viewer.)