spousal equivalent vs significant other

spousal equivalent and significant other both are nouns.

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

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

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

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

spousal 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