drier vs hair drier

drier and hair drier both are nouns.

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

As nouns, hair drier is a hyponym of drier; that is, hair drier is a word with a more specific, narrower meaning than drier:

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

drier (noun)	hair drier (noun)
an appliance that removes moisture	a hand-held electric blower that can blow warm air onto the hair; used for styling hair
a substance that promotes drying (e.g., calcium oxide absorbs water and is used to remove moisture)