Is hardhat one word or two?

Answer 1

Reputable dictionaries of American English list it three ways: hard hat; hard-hat; hardhat. The choice seems to rest partly on the meaning of the phase and how it is used grammatically. If the main reference is to a hat such as a protective helmet that happens to be hard, then it will be "hard hat." If it is slang for "a construction worker" or "an ultra conservative person," then it may be "hard-hat" or "hardhat." If it used as an adjective ("CAUTION: Hard-hat area") then it will be "hard-hat" or "hardhat." If used as a noun ("CAUTION: Hard hat required") then is may appear as two words. Words of that kind usually pass through stages, beginning as two words, developing into hyphenated forms, and then finally finding acceptance as fused single words.