Plural of Octopus

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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).

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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 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.)
Another Interactive Exercise
Here are three randomly selected questions from another exercise on plurals, which can be edited, printed to create an exercise worksheet, or sent via email to friends or students.

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See Also

Unusual pluralsPlural forming table Quirks with forming plurals Forming the plurals of abbreviations Forming the plurals of compound nouns