mainstay vs lynchpin

mainstay and lynchpin both are nouns.

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

As nouns, mainstay and lynchpin are synonyms defined as:

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

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

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