unbend vs loosen up

unbend and loosen up both are verbs.

Word	Noun	Adjective	Verb	Adverb
unbend	No	No	Yes	No
loosen up	No	No	Yes	No

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

Other hypernyms of unbend include make relaxed, relax, unlax, unstrain, unwind.

As verbs, unbend and loosen up are synonyms defined as:

Other synonyms of unbend include decompress, relax, slow down, unwind.

unbend (verb)	loosen up (verb)
release from mental strain, tension, or formality	become less tense, rest, or take one's ease
become less tense, rest, or take one's ease	cause to feel relaxed
make less taut	make one's body limber or suppler by stretching, as if to prepare for strenuous physical activity
free from flexure	cause to become unblocked
unfasten, as a sail, from a spar or a stay	become less tense, less formal, or less restrained, and assume a friendlier manner
straighten up or out; make straight