supporter vs mainstay

supporter and mainstay both are nouns.

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

As nouns, mainstay is a hyponym of supporter; that is, mainstay is a word with a more specific, narrower meaning than supporter:

supporter (noun)	mainstay (noun)
a band (usually elastic) worn around the leg to hold up a stocking (or around the arm to hold up a sleeve)	the forestay that braces the mainmast
a support for the genitals worn by men engaging in strenuous exercise	a central cohesive source of support and stability
a person who backs a politician or a team etc.	a prominent supporter
a person who contributes to the fulfillment of a need or furtherance of an effort or purpose
someone who supports or champions something