old man vs hirer

old man and hirer both are nouns.

Word	Noun	Adjective	Verb	Adverb
old man	Yes	No	No	No
hirer	Yes	No	No	No

As nouns, hirer is a hypernym of old man; that is, hirer is a word with a broader meaning than old man:

Other hypernyms of old man include boss.

old man (noun)	hirer (noun)
an informal term for your father	a person responsible for hiring workers
a man who is very old
a familiar term of address for a man
(slang) boss
aromatic herb of temperate Eurasia and North Africa having a bitter taste used in making the liqueur absinthe