ancestor vs sire

ancestor and sire both are nouns.

Word	Noun	Adjective	Verb	Adverb
ancestor	Yes	No	No	No
sire	Yes	No	Yes	No

As nouns, sire is a hyponym of ancestor; that is, sire is a word with a more specific, narrower meaning than ancestor:

ancestor: someone from whom you are descended (but usually more remote than a grandparent)
sire: the founder of a family

Other hyponyms of ancestor include ancestress, forbear, forebear, father, forefather, foremother, primogenitor, progenitor.

ancestor (noun)	sire (noun)
someone from whom you are descended (but usually more remote than a grandparent)	male parent of an animal especially a domestic animal such as a horse
	the founder of a family
	a title of address formerly used for a man of rank and authority

ancestor (verb)	sire (verb)
	make (offspring) by reproduction