lover vs domestic partner

lover and domestic partner both are nouns.

Word	Noun	Adjective	Verb	Adverb
lover	Yes	No	No	No
domestic partner	Yes	No	No	No

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

lover: a significant other to whom you are not related by marriage
domestic partner: a person (not necessarily a spouse) with whom you cohabit and share a long-term sexual relationship

Other hypernyms of lover include significant other, spousal equivalent, spouse equivalent.

lover (noun)	domestic partner (noun)
a person who loves someone or is loved by someone	a person (not necessarily a spouse) with whom you cohabit and share a long-term sexual relationship
an ardent follower and admirer
a significant other to whom you are not related by marriage