lynchpin vs keystone

lynchpin and keystone both are nouns.

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

As nouns, lynchpin and keystone are synonyms defined as:

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

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

lynchpin (noun)	keystone (noun)
pin inserted through an axletree to hold a wheel on	the central building block at the top of an arch or vault
a central cohesive source of support and stability	a central cohesive source of support and stability