spouse equivalent vs significant other

spouse equivalent and significant other both are nouns.

Word	Noun	Adjective	Verb	Adverb
spouse equivalent	Yes	No	No	No
significant other	Yes	No	No	No

As nouns, spouse equivalent and significant other are synonyms defined as:

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

Other synonyms of spouse equivalent include domestic partner, spousal equivalent.

spouse equivalent (noun)	significant other (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