significant other vs actor

significant other and actor both are nouns.

Word	Noun	Adjective	Verb	Adverb
significant other	Yes	No	No	No
actor	Yes	No	No	No

As nouns, actor is a hypernym of significant other; that is, actor is a word with a broader meaning than significant other:

significant other: a person (not necessarily a spouse) with whom you cohabit and share a long-term sexual relationship
actor: a person who acts and gets things done

Other hypernyms of significant other include doer, worker.

significant other (noun)	actor (noun)
a person (not necessarily a spouse) with whom you cohabit and share a long-term sexual relationship	a theatrical performer
	a person who acts and gets things done