partner vs domestic partner

partner and domestic partner both are nouns.

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

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

partner: a person's partner in marriage
domestic partner: a person (not necessarily a spouse) with whom you cohabit and share a long-term sexual relationship

Other hypernyms of partner include significant other, spousal equivalent, spouse equivalent, relation, relative.

partner (noun)	domestic partner (noun)
an associate in an activity or endeavor or sphere of common interest	a person (not necessarily a spouse) with whom you cohabit and share a long-term sexual relationship
a person's partner in marriage
a person who is a member of a partnership

partner (verb)	domestic partner (verb)
provide with a partner
act as a partner