old geezer vs greybeard

old geezer and greybeard both are nouns.

Word	Noun	Adjective	Verb	Adverb
old geezer	Yes	No	No	No
greybeard	Yes	No	No	No

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

Other hypernyms of old geezer include graybeard, Methuselah, old man.

old geezer (noun)	greybeard (noun)
an elderly man	a stoneware drinking jug with a long neck; decorated with a caricature of Cardinal Bellarmine (17th century)
	a man who is very old