significant other vs domestic partner

significant other and domestic partner both are nouns.

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

As nouns, significant other and domestic partner are synonyms defined as:

significant other and domestic partner: a person (not necessarily a spouse) with whom you cohabit and share a long-term sexual relationship

Other synonyms of significant other include spousal equivalent, spouse equivalent.

significant other (noun)	domestic partner (noun)
a person (not necessarily a spouse) with whom you cohabit and share a long-term sexual relationship	a person (not necessarily a spouse) with whom you cohabit and share a long-term sexual relationship