old man vs codger

old man and codger both are nouns.

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

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

Other hyponyms of old man include old codger, antique, gaffer, old-timer, old geezer, oldtimer, patriarch.

old man (noun)	codger (noun)
an informal term for your father	used affectionately to refer to an eccentric but amusing old man
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