prune vs cut back

prune is a noun but cut back is not a noun.

Word	Noun	Adjective	Verb	Adverb
prune	Yes	No	Yes	No
cut back	No	No	Yes	No

As verbs, prune and cut back are synonyms defined as:

Other synonyms of prune include clip, crop, dress, lop, snip, trim.

prune (noun)	cut back (noun)
dried plum

prune (verb)	cut back (verb)
weed out unwanted or unnecessary things	place restrictions on
cultivate, tend, and cut back the growth of	cut down on; make a reduction in
	cultivate, tend, and cut back the growth of
	return in time