betrothed vs lover

betrothed and lover both are nouns.

Word	Noun	Adjective	Verb	Adverb
betrothed	Yes	Yes	No	No
lover	Yes	No	No	No

As nouns, lover is a hypernym of betrothed; that is, lover is a word with a broader meaning than betrothed:

betrothed (noun)	lover (noun)
the person to whom you are engaged	a person who loves someone or is loved by someone
	an ardent follower and admirer
	a significant other to whom you are not related by marriage

betrothed (adjective)	lover (adjective)
pledged to be married