hair drier vs dryer

hair drier and dryer both are nouns.

Word	Noun	Adjective	Verb	Adverb
hair drier	Yes	No	No	No
dryer	Yes	No	No	No

As nouns, dryer is a hypernym of hair drier; that is, dryer is a word with a broader meaning than hair drier:

hair drier: a hand-held electric blower that can blow warm air onto the hair; used for styling hair
dryer: an appliance that removes moisture

Other hypernyms of hair drier include blower, drier.

hair drier (noun)	dryer (noun)
a hand-held electric blower that can blow warm air onto the hair; used for styling hair	an appliance that removes moisture