straighten vs comb

straighten is not a noun while comb is a noun.

Word	Noun	Adjective	Verb	Adverb
straighten	No	No	Yes	No
comb	Yes	No	Yes	No

As verbs, comb is a hyponym of straighten; that is, comb is a word with a more specific, narrower meaning than straighten:

Other hyponyms of straighten include untwist, unbend, extend, channelise, channelize, untwine, unweave.

straighten (noun)	comb (noun)
	the act of drawing a comb through hair
	ciliated comb-like swimming plate of a ctenophore
	the fleshy red crest on the head of the domestic fowl and other gallinaceous birds
	a flat device with narrow pointed teeth on one edge; disentangles or arranges hair
	any of several tools for straightening fibers

straighten (verb)	comb (verb)
put (things or places) in order	smoothen and neaten with or as with a comb
make straight or straighter	search thoroughly
make straight	straighten with a comb
straighten by unrolling
straighten up or out; make straight
get up from a sitting or slouching position