furthest vs comparative degree

furthest is not a noun while comparative degree is a noun.

Word	Noun	Adjective	Verb	Adverb
furthest	No	Yes	No	Yes
comparative degree	Yes	No	No	No

furthest (noun)	comparative degree (noun)
	the comparative form of an adjective or adverb

furthest (adjective)	comparative degree (adjective)
(comparatives of `far') most remote in space or time or order

furthest (adverb)	comparative degree (adverb)
to the greatest distance in space or time (`farthest' is used more often than `furthest' in this physical sense)
to the greatest degree or extent or most advanced stage (`furthest' is used more often than `farthest' in this abstract sense)