superfluous vs extra

superfluous is not a noun while extra is a noun.

Word	Noun	Adjective	Verb	Adverb
superfluous	No	Yes	No	No
extra	Yes	Yes	No	Yes

As adjectives, superfluous and extra are synonyms defined as:

Other synonyms of superfluous include excess, redundant, spare, supererogatory, supernumerary, surplus.

superfluous (noun)	extra (noun)
	something additional of the same kind
	an additional edition of a newspaper (usually to report a crisis)
	a minor actor in crowd scenes

superfluous (adjective)	extra (adjective)
more than is needed, desired, or required	further or added
serving no useful purpose; having no excuse for being	more than is needed, desired, or required
	added to a regular schedule

superfluous (adverb)	extra (adverb)
	unusually or exceptionally