loosen up vs unbend

loosen up and unbend both are verbs.

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

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

Other synonyms of loosen up include decompress, relax, slow down, unwind.

As verbs, unbend is a hyponym of loosen up; that is, unbend is a word with a more specific, narrower meaning than loosen up:

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