omissible vs incidental

omissible is not a noun while incidental is a noun.

Word	Noun	Adjective	Verb	Adverb
omissible	No	Yes	No	No
incidental	Yes	Yes	No	No

omissible (noun)	incidental (noun)
	an item that is incidental
	(frequently plural) an expense not budgeted or not specified

omissible (adjective)	incidental (adjective)
capable of being left out	(sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence
	not of prime or central importance
	occurring with or following as a consequence