-o

-o

1. Plurals of nouns ending in -o cause difficulty in English because there are few convenient rules for choosing between -os (as in ratios) and -oes (as in heroes). What rules there are can be briefly summarized:

a) When a vowel (usually i or e) precedes the final -o, the plural is normally -os (trios, videos), probably because of the bizarre look of -ioes etc.

b) Names of animals and plants normally form plurals in -oes (buffaloes, tomatoes).

c) Words that are shortenings of other words invariably form plurals in -os (demos, hippos). The same applies to fanciful extensions such as saddo (plural saddos).

d) Alien-looking words and comparatively recent loanwords form plurals in -os (boleros, placebos).

e) Multi-syllable words tend to form plurals in -os (generalissimos, manifestos).

f) Proper names form plurals (used allusively) in -os (Neros, Romeos).

2. In other cases, practice varies from one house style to another, and the table below gives a consensus of informed usage.

singular / plural

alto / altos

banjo / banjos

buffalo / buffaloes

cargo / cargoes

casino / casinos

concerto / concertos or concerti

contralto / contraltos

do / dos or do's

dodo / dodos

domino / dominoes

dynamo / dynamos

echo / echoes

ego / egos

embargo / embargoes

fiasco / fiascos

flamingo / flamingos

fresco / frescos

gigolo / gigolos

go / goes

grotto / grottoes

hairdo / hairdos

halo / haloes

hero / heroes

hippo / hippos

innuendo / innuendoes

kilo / kilos

libretto / librettos

mango / mangoes

manifesto / manifestos

memento / mementoes

memo / memos

mosquito / mosquitoes

motto / mottoes

Negro / Negroes

no / noes

peccadillo / peccadilloes

photo / photos

piano / pianos

piccolo / piccolos

potato / potatoes

proviso / provisos

radio / radios

rhino / rhinos, or (collective) rhino

salvo (= firing of guns) / salvoes

silo / silos

solo / solos

soprano / sopranos

stiletto / stilettos

tiro / tiros

tobacco / tobaccos

tomato / tomatoes

torpedo / torpedoes

verso / versos

veto / vetoes

volcano / volcanoes

zero / zeros