Cambridge Grammar of English Hardback with cd-rom a comprehensive Guide

Writing compound nouns

Familiar compound nouns (usually those involving short, monosyllabic nouns)

are normally written as one word:

postman

bathroom

lampshade

There is some inconsistency, however. Some compounds are written with a

hyphen:

pen-friend

tee-shirt

belly-dancing

In the case of some pairs, hyphens, separate words and words joined together are

all equally possible:

post-box

post box

postbox

Normally, if a compound is perceived as a single word, it tends to be written as a

whole word without a space or a hyphen. Hyphenation is less common in

American than in British English. 

Û

265 Compounds for further information on noun compounds 

Û

507–511 Appendix: English spelling for spelling and use of hyphens and

apostrophes involving noun compounds and other types of compound