recoil vs shrink back

recoil is a noun but shrink back is not a noun.

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

As verbs, shrink back is a hyponym of recoil; that is, shrink back is a word with a more specific, narrower meaning than recoil:

Other hyponyms of recoil include retract.

recoil (noun)	shrink back (noun)
a movement back from an impact
the backward jerk of a gun when it is fired

recoil (verb)	shrink back (verb)
spring back, as from a forceful thrust	pull away from a source of disgust or fear
draw back, as with fear or pain
spring back; spring away from an impact
come back to the originator of an action with an undesired effect