bend vs straighten

bend is a noun but straighten is not a noun.

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

bend (noun)	straighten (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

bend (verb)	straighten (verb)
cause (an object) to assume a crooked or angular form	put (things or places) in order
bend a joint	make straight or straighter
form a curve	make straight
change direction	straighten by unrolling
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	get up from a sitting or slouching position