curb vs cut back

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

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

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

Other synonyms of curb include curtail, restrict.

curb (noun)	cut back (noun)
the act of restraining power or action or limiting excess
an edge between a sidewalk and a roadway consisting of a line of curbstones (usually forming part of a gutter)
a horse's bit with an attached chain or strap to check the horse

curb (verb)	cut back (verb)
place restrictions on	place restrictions on
keep to the curb	cut down on; make a reduction in
lessen the intensity of; temper; hold in restraint; hold or keep within limits	cultivate, tend, and cut back the growth of
	return in time