old man vs begetter

old man and begetter both are nouns.

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

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

Other hypernyms of old man include dysphemism, father, male parent.

old man (noun)	begetter (noun)
an informal term for your father	a male parent (also used as a term of address to 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