incidental vs parenthetical

incidental and parenthetical both are nouns.

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

incidental (noun)	parenthetical (noun)
an item that is incidental	an expression in parentheses
(frequently plural) an expense not budgeted or not specified

incidental (adjective)	parenthetical (adjective)
(sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence	qualifying or explaining; placed or as if placed in parentheses
not of prime or central importance
occurring with or following as a consequence