shrink back vs wince

shrink back is not a noun while wince is a noun.

Word	Noun	Adjective	Verb	Adverb
shrink back	No	No	Yes	No
wince	Yes	No	Yes	No

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

Other hypernyms of shrink back include cringe, flinch, funk, quail, recoil, shrink, squinch.

shrink back (noun)	wince (noun)
	a reflex response to sudden pain
	the facial expression of sudden pain

shrink back (verb)	wince (verb)
pull away from a source of disgust or fear	make a face indicating disgust or dislike
	draw back, as with fear or pain