frivolous vs idle

frivolous is not a noun while idle is a noun.

Word	Noun	Adjective	Verb	Adverb
frivolous	No	Yes	No	No
idle	Yes	Yes	Yes	No

frivolous (noun)	idle (noun)
	the state of an engine or other mechanism that is idling

frivolous (adjective)	idle (adjective)
not serious in content or attitude or behavior	not in action or at work
	silly or trivial
	not in active use
	lacking a sense of restraint or responsibility
	not having a job
	not yielding a return
	without a basis in reason or fact

frivolous (verb)	idle (verb)
	run disconnected or idle
	be idle; exist in a changeless situation