warm the bench vs idle

warm the bench is not a noun while idle is a noun.

Word	Noun	Adjective	Verb	Adverb
warm the bench	No	No	Yes	No
idle	Yes	Yes	Yes	No

As verbs, idle is a hypernym of warm the bench; that is, idle is a word with a broader meaning than warm the bench:

Other hypernyms of warm the bench include laze, slug, stagnate.

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

warm the bench (adjective)	idle (adjective)
	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

warm the bench (verb)	idle (verb)
be out of the game	run disconnected or idle
	be idle; exist in a changeless situation