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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 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 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.)