Real Dictionary

hard hat
countable noun: A hard hat is a hat made from a hard material, which people wear to protect their heads on building sites or in factories, or when riding a horse.

hard hat in American English
a protective helmet worn by construction workers, miners, etc.
noun: a protective helmet of metal or plastic, esp. as worn by construction or factory workers

hard hat in British English
adjective: characteristic of the presumed conservative attitudes and prejudices typified by construction workers
noun: a hat made of a hard material for protection, worn esp by construction workers, equestrians, etc

hard-hat in American English
adjective: pertaining to or characteristic of hard-hats
noun: a construction worker, esp. a member of a construction workers' union

hard-hat in British English
adjective: characteristic of the presumed conservative attitudes and prejudices typified by construction workers