unbend vs bend

unbend is not a noun while bend is a noun.

Word	Noun	Adjective	Verb	Adverb
unbend	No	No	Yes	No
bend	Yes	No	Yes	No

unbend (noun)	bend (noun)
	curved segment (of a road or river or railroad track etc.)
	diagonal line traversing a shield from the upper right corner to the lower left
	movement that causes the formation of a curve
	an angular or rounded shape made by folding
	a circular segment of a curve

unbend (verb)	bend (verb)
release from mental strain, tension, or formality	cause (an object) to assume a crooked or angular form
become less tense, rest, or take one's ease	bend a joint
make less taut	form a curve
free from flexure	change direction
unfasten, as a sail, from a spar or a stay	turn from a straight course, fixed direction, or line of interest
straighten up or out; make straight	bend one's back forward from the waist on down