old woman vs beldam

old woman and beldam both are nouns.

Word	Noun	Adjective	Verb	Adverb
old woman	Yes	No	No	No
beldam	Yes	No	No	No

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

Other hyponyms of old woman include beldame, granny, beldame, crone, hag, witch, mother.

old woman (noun)	beldam (noun)
a woman who is old	a woman of advanced age
herb with greyish leaves found along the east coast of North America; used as an ornamental plant	an ugly evil-looking old woman