quoin vs keystone

quoin and keystone both are nouns.

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

As nouns, keystone is a hypernym of quoin; that is, keystone is a word with a broader meaning than quoin:

Other hypernyms of quoin include headstone, key.

quoin (noun)	keystone (noun)
(architecture) solid exterior angle of a building; especially one formed by a cornerstone	the central building block at the top of an arch or vault
the keystone of an arch	a central cohesive source of support and stability
expandable metal or wooden wedge used by printers to lock up a form within a chase