unbend vs straighten

unbend and straighten both are verbs.

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

As verbs, straighten is a hypernym of unbend; that is, straighten is a word with a broader meaning than unbend:

Other hypernyms of unbend include straighten out.

As verbs, unbend and straighten are synonyms defined as:

unbend (verb)	straighten (verb)
release from mental strain, tension, or formality	put (things or places) in order
become less tense, rest, or take one's ease	make straight or straighter
make less taut	make straight
free from flexure	straighten by unrolling
unfasten, as a sail, from a spar or a stay	straighten up or out; make straight
straighten up or out; make straight	get up from a sitting or slouching position