mainstay vs friend

mainstay and friend both are nouns.

Word	Noun	Adjective	Verb	Adverb
mainstay	Yes	No	No	No
friend	Yes	No	No	No

As nouns, friend is a hypernym of mainstay; that is, friend is a word with a broader meaning than mainstay:

Other hypernyms of mainstay include admirer, booster, champion, protagonist, supporter.

mainstay (noun)	friend (noun)
the forestay that braces the mainmast	a person you know well and regard with affection and trust
a central cohesive source of support and stability	a person with whom you are acquainted
a prominent supporter	an associate who provides cooperation or assistance
	a person who backs a politician or a team etc.