PLURAL RULES

PLURAL RULE 1 - Most Words add 's' to make the Plural:

The plural form of most nouns is created simply by adding the letter 's'.

more than one snake = snakes
more than one ski = skis
more than one Barrymore = Barrymores

Words that end in -ch, x, s or s-like sounds, however, will require an -es for the plural:

more than one witch = witches
more than one box = boxes
more than one gas = gases
more than one bus = buses
more than one kiss = kisses
more than one Jones = Joneses

Note that some dictionaries list "busses" as an acceptable plural for "bus." Presumably, this is because the plural "buses" looks like it ought to rhyme with the plural of "fuse," which is "fuses." "Buses" is still listed as the preferable plural form. "Busses" is the plural, of course, for "buss," a seldom used word for "kiss."


http://grammar.ccc.commnet.edu/grammar/plurals.htm