Plural of Platypus

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).

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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 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	donkeys 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

Read more about English spelling rules.

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.)