supererogatory vs supernumerary

supererogatory is not a noun while supernumerary is a noun.

Word	Noun	Adjective	Verb	Adverb
supererogatory	No	Yes	No	No
supernumerary	Yes	Yes	No	No

As adjectives, supererogatory and supernumerary are synonyms defined as:

supererogatory and supernumerary: more than is needed, desired, or required

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

supererogatory (noun)	supernumerary (noun)
	a minor actor in crowd scenes
	a person serving no apparent function

supererogatory (adjective)	supernumerary (adjective)
more than is needed, desired, or required	more than is needed, desired, or required