cut back vs decrease

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

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

As verbs, decrease is a hypernym of cut back; that is, decrease is a word with a broader meaning than cut back:

Other hypernyms of cut back include lessen, minify.

cut back (noun)	decrease (noun)
	the act of decreasing or reducing something
	the amount by which something decreases
	a change downward
	a process of becoming smaller or shorter

cut back (verb)	decrease (verb)
place restrictions on	decrease in size, extent, or range
cut down on; make a reduction in	make become smaller
cultivate, tend, and cut back the growth of
return in time