linchpin vs mainstay

linchpin and mainstay both are nouns.

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

As nouns, linchpin and mainstay are synonyms defined as:

linchpin and mainstay: a central cohesive source of support and stability

Other synonyms of linchpin include anchor, backbone, keystone, lynchpin.

linchpin (noun)	mainstay (noun)
pin inserted through an axletree to hold a wheel on	the forestay that braces the mainmast
a central cohesive source of support and stability	a central cohesive source of support and stability
	a prominent supporter