hair shirt vs shirt

hair shirt and shirt both are nouns.

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

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

hair shirt: an uncomfortable shirt made of coarse animal hair; worn next to the skin as a penance
shirt: a garment worn on the upper half of the body

hair shirt (noun)	shirt (noun)
an uncomfortable shirt made of coarse animal hair; worn next to the skin as a penance	a garment worn on the upper half of the body

hair shirt (verb)	shirt (verb)
	put a shirt on