In English, we make frequent use of compounding, where we combine
two or more words—sometimes with intervening spaces, sometimes with
the use of a hyphen, "-", and sometimes with the use of an additional
letter or two (and, in a few cases dropping a letter)—to form what is
effectively a longer word. Compounding is used for words of all types:
nouns and verbs, pronouns, qualifiers such as adjectives and adverbs, and
prepositions as well. Examples are
adjectives: rearview (rear + view) as in "rearview mirror"; ice-cream:
compounding with hyphenation is used when a compounded noun becomes an
adjective, as in "ice-cream sandwich";
adverbs: indoor (in + door); altogether (all + together);
prepositions: without (with + out).
The plurals of compounded nouns without hyphens are obtained by adding the
letter s: for instance,
windshields,
grandmothers, and
ice creams. For hyphenated compounding, the
situation is more complicated, and appears to be a mix of logic and
tradition: brothers-in-law and
commanders-in-chief are considered
correct plurals, while both jacks-in-the-box and
jack-in-the-boxes are considered correct plurals.