Plural of Octopus

The Quick Answer

The plural of octopus is octopuses.

The Plural of Octopus

The plural of octopus is octopuses.

Octopuses have a relatively short life expectancy, with some species living for as little as six months.
Large octopuses have been known to catch and kill some species of sharks.

The noun octopus has a Greek root. The Greek plural for octopus is octopodes, but this plural is not used in English. The plural octopi is used by people who mistakenly believe that octopus has a Latin derivation, meaning its plural would be octopi (in the same way that fungus, cactus, and hippopotamus become fungi, cacti, and hippopotami).

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	octopus dress	add es	octopuses 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

Why Is There Confusion over the Plural of Octopus?

Confusion arises over the plural of octopus 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), octopi is becoming an accepted plural for octopus. Nevertheless, the safest version to use is octopuses. (See the difference in Google's Ngram Viewer.)

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