cut back vs curb

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

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

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

Other synonyms of cut back include curtail, restrict.

cut back (noun)	curb (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

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