shrink back vs retract

shrink back and retract both are verbs.

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

As verbs, shrink back and retract are synonyms defined as:

shrink back (verb)	retract (verb)
pull away from a source of disgust or fear	formally reject or disavow a formerly held belief, usually under pressure
	pull inward or towards a center
	use a surgical instrument to hold open (the edges of a wound or an organ)
	pull away from a source of disgust or fear