Irregular in spelling only: nouns ending in –o

a Add the letters es to a base ending in the letter o:

potatoes, echoes, embargoes, heroes, mottoes, negroes, tomatoes, torpedoes, vetoes.

The e is optional in:

Buffalo(e)s, cargo(e)s, commando(e)s, grotto(e)s, halo(e)s, mosquito(e)s, tornado(e)s, volcano(e)s.

b The following do not have e in the spelling:

i nouns ending in the singular in o preceded by any vowel letter or vowel sound:

bamboos, embryos, folios, kangaroos, oratorios, radios, zoos

ii abbreviations, eg

kilos (= kilograms), memos (= memoranda), photos (= photographs)

iii musical terms of Italian origin:

concertos, contraltos, pianos, solos, sopranos

iv proper names, eg

Eskimos, Filipinos

v dynamos.

Irregular in both pronunciation and spelling