hirer vs old man

hirer and old man both are nouns.

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

As nouns, old man is a hyponym of hirer; that is, old man is a word with a more specific, narrower meaning than hirer:

Other hyponyms of hirer include guvnor.

hirer (noun)	old man (noun)
a person responsible for hiring workers	an informal term for your father
	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