incidental vs secondary

incidental and secondary both are nouns.

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

incidental (noun)	secondary (noun)
an item that is incidental	coil such that current is induced in it by passing a current through the primary coil
(frequently plural) an expense not budgeted or not specified	the defensive football players who line up behind the linemen

incidental (adjective)	secondary (adjective)
(sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence	being of second rank or importance or value; not direct or immediate
not of prime or central importance	depending on or incidental to what is original or primary
occurring with or following as a consequence	inferior in rank or status
	not of major importance
	belonging to a lower class or rank