extra vs superfluous

extra is a noun but superfluous is not a noun.

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

As adjectives, extra and superfluous are synonyms defined as:

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

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

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

extra (adverb)	superfluous (adverb)
unusually or exceptionally