trim vs cut back

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

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

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

Other synonyms of trim include bring down, cut, cut down, reduce, trim back, trim down.

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

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

trim (noun)	cut back (noun)
cutting down to the desired size or shape
a decoration or adornment typically on the edge of a garment
attitude of an aircraft in flight when allowed to take its own orientation
a state of arrangement or appearance

trim (adjective)	cut back (adjective)
severely simple in line or design
thin and fit
characterized by order and neatness; free from disorder
neat and smart in appearance

trim (verb)	cut back (verb)
cut down on; make a reduction in	place restrictions on
adjust (sails on a ship) so that the wind is optimally used	cut down on; make a reduction in
cut closely	cultivate, tend, and cut back the growth of
cultivate, tend, and cut back the growth of	return in time
remove the edges from and cut down to the desired size
decorate (food), as with parsley or other ornamental foods
decorate, as with ornaments
be in equilibrium during a flight
balance in flight by regulating the control surfaces