The following words and their plurals seem to be somewhat inconsistent:

  • combo / combos
  • concerto / concertos
  • grotto / grottos / grottoes (?)
  • hero / heros (?) / heroes
  • potato / potatos (?) / potatoes
  • tornado / tornados / tornadoes
  • tomato / tomatos / tomatoes
  • volcano / volcanos / volcanoes

Is there a common source for -s versus -es? With regards to words such as "heros", is it likely to see more words start dropping -es in favor of -s?

(If you have any other good examples of strange plurals from words ending in "o" feel free to edit them into the question.)

  • I don't think you can include "combo" in that list. It's slang for "combination". – user362 Apr 29 '11 at 16:28
  • 4
    @Al: "Combo" has its own entry in my dictionary along with a rule for pluralizing it. It being slang for "combination" is likely why it gets -s instead of -es which, presumably, would be part of the answer to this question. But "combo" is a word and it is pluralized and it does end in "o". Therefore, I consider it relevant to this question. – MrHen Apr 29 '11 at 16:35
  • I think Al has it right: combo is slang and that's why it's irregular. All the others are -oes. – Malvolio Apr 29 '11 at 16:37
  • @Al, @Mal: If you think that is the answer than post it as an answer. :) Simple but correct answers are still correct. But I am still curious about potatos. – MrHen Apr 29 '11 at 16:40
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    Never seen it spelled "potatos". – user362 Apr 29 '11 at 16:51

This is what The Cambridge Grammar of the English Language (p. 1586, The alternation between ·s and ·es) has to say about it:

With bases ending in o, where o does not follow a consonant symbol (i.e. where it is preceded by a vowel or is part of the composite vowel symbol oo), the plural takes ·s:

bamboos, cameos, embryos, folios, kangaroos, patios, radios, studios, zoos

Where o does follow a consonant, the plural has to be specified for the lexeme concerned. There are three classses:

i. ·es only: echo ~ echoes. Also domino, embargo, hero, mango, negro, potato, tomato, torpedo, veto

ii. ·s or ·es: motto ~ mottos/mottoes. Also, archipelago, banjo, buffalo, cargo, dado, dodo, grotto, halo, innuendo, manifesto, mulatto, proviso, tornado, volcano

iii. ·s only: bistro ~ bistros. Also calypso, do, dynamo, beano; clippings such as demo, kilo, memo, photo; nouns of Italian origin: cello, concerto, contralto, libretto, maestro, piano, quarto, solo, soprano, virtuoso; and names of ethnic groups: Chicano, Eskimo, Filipino, Texano.

Cargo and volcano are marginal members of class [ii]: they usually take ·es, but the forms cargos and volcanos are sometimes found.

As an additional rule of thumb, almost of all the exceptions for the consonant + o + s = es rule seem to involve plural nouns where there is no homophonous verb, as per CGEL, p. 1580.

For class [ii], it might be useful to use Google Books Ngram Viewer to assess the ·ses distribution, and to go with the ending that seems to be preferred in literary sources. For instance,

Google Books Ngram Viewer — mottos vs mottoes — English enter image description here Google Books Ngram Viewer — banjos vs banjoes — English enter image description here


Actually I do believe that the rule is:

  • -oes for most words ending in -o: potatoes, tomatoes
  • -os for any words related (usually) to music (i.e. loanwords, from Italian). These would include: pianos, crescendos, radios, concertos, sopranos, pimentos (loanword), etc.
  • It's not strictly a rule since you'll find exceptions. It is however a useful guideline that is correct much of the time. – Jon Hanna Jan 16 '13 at 11:39

If the noun ends with vowel + o, just add -s: radios, zoos.

If it’s a music word, it’s probably Italian, so just add -s: pianos, concertos.

Otherwise, look it up in a dictionary. There is no rule of thumb that correctly covers all words. Many nouns ending with -o can take either -es or -s but one or the other is preferred.

(This answer is informed by a recent attempt of mine to boil down CGEL’s spelling rules for plurals and suffixes to something my kids could memorize. CGEL is the Cambridge Grammar of the English Langauge. I was not all that successful.)


To complete the accepted answer, I found a similar, but more extensive information in Oxford dictionaries -> Plural of nouns:

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:

singular    plural
solo        solos
zero        zeros
avocado     avocados

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

singular    plural
studio      studios
zoo         zoos
embryo      embryos

Here’s a list of the most common nouns ending in -o that are always spelled with -es in the plural:

singular    plural
buffalo     buffaloes
domino      dominoes
echo        echoes
embargo     embargoes
hero        heroes
mosquito    mosquitoes
potato      potatoes
tomato      tomatoes
torpedo     torpedoes
veto        vetoes

Here are some of the common nouns ending in -o that can be spelled with either -s or -es in the plural:

singular    plural
banjo       banjos    or banjoes
cargo       cargos    or cargoes
flamingo    flamingos or flamingoes
fresco      frescos   or frescoes
ghetto      ghettos   or ghettoes
halo        halos     or haloes
mango       mangos    or mangoes
memento     mementos  or mementoes
motto       mottos    or mottoes
tornado     tornados  or tornadoes
tuxedo      tuxedos   or tuxedoes
volcano     volcanos  or volcanoes

Just a wild guess from an observation on your examples:

  • two consonants before the -o gives -os;
  • one consonant before the -o gives -oes;

Although checking the dictionary reveals that both spelling are correct. Could be British/American English thing?

protected by RegDwigнt Jan 16 '13 at 11:09

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