unused vs idle

unused is not a noun while idle is a noun.

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

As adjectives, unused and idle are synonyms defined as:

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

unused (adjective)	idle (adjective)
not yet used or soiled	not in action or at work
not in active use	silly or trivial
not yet put into use	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

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