incidental vs accompanying

incidental is a noun but accompanying is not a noun.

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

As adjectives, incidental and accompanying are synonyms defined as:

incidental and accompanying: occurring with or following as a consequence

Other synonyms of incidental include attendant, collateral, concomitant, consequent, ensuant, resultant, sequent.

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

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