sit back vs unwind

sit back and unwind both are verbs.

Word	Noun	Adjective	Verb	Adverb
sit back	No	No	Yes	No
unwind	No	No	Yes	No

As verbs, unwind is a hypernym of sit back; that is, unwind is a word with a broader meaning than sit back:

Other hypernyms of sit back include decompress, loosen up, relax, slow down, unbend.

sit back (verb)	unwind (verb)
settle into a comfortable sitting position	become less tense, rest, or take one's ease
be inactive or indifferent while something is happening	cause to feel relaxed
	separate the tangles of
	reverse the winding or twisting of