The rule says that if a singular noun ends in consonant + "o" then the plural form will be consonant + "oes".

e.g. tomato => tomatoes.

Then, why this rule does not apply to piano?

  • 1
    The exception proves the rule. "Piano" is a word of Italian origin and Italian words ending in "o" form the plural by adding only "s". The same for "casino" casino - casinos – Centaurus Jul 21 '17 at 16:06
  • 7
    Because the First Rule in the English language is that no rule works 100% of the time. And when I say "no rule" I include the First Rule... – AndyT Jul 21 '17 at 16:07
  • 2
    The rule is wrong. English spelling is chaotic and has to be learned individually. Don't trust any English spelling rules; there will always be many exceptions (and anyone who states the rule will never tell you all of them, because they don't know, either). – John Lawler Jul 21 '17 at 16:15
  • Geese, moose, sheep to name a few other random pluralisations – marcellothearcane Jul 21 '17 at 17:53

Plural of nouns ending in -o:

Nouns ending in -o can add either -s or -es in the plural, and some can be spelled either way.

As a general rule, most nouns ending in -o add -s to make the plural:

So you have:

solo solos, zero zeros, avocado avocados

Note that:

Those which have a vowel before the final -o always just add -s:


studio studios, zoo zoos, embryo embryos.


piano, pianos

Oxford Dictionary

  • 5
    You just missed answering the question and still it is accepted - that's bizarre. "Those which have a vowel before the final -o always just add -s like studio studios etc." So piano pianos? How is n a vovel? The link thankfully is correct and it has specific examples of words ending with a consonants followed by a vowel using es as suffix for plural, like domino dominoes. – Nikhil Girraj Jul 26 '17 at 17:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.