shrink back vs shrink

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

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

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

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

shrink back (noun)	shrink (noun)
	a physician who specializes in psychiatry

shrink back (verb)	shrink (verb)
pull away from a source of disgust or fear	become smaller or draw together
	reduce in size; reduce physically
	wither, as with a loss of moisture
	decrease in size, range, or extent
	draw back, as with fear or pain