old codger vs old man

old codger and old man both are nouns.

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

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

old codger: used affectionately to refer to an eccentric but amusing old man
old man: a man who is very old

Other hypernyms of old codger include graybeard, greybeard, Methuselah.

old codger (noun)	old man (noun)
used affectionately to refer to an eccentric but amusing old man	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