secondary vs incidental

secondary and incidental both are nouns.

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

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

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