keep back vs refuse

keep back is not a noun while refuse is a noun.

Word	Noun	Adjective	Verb	Adverb
keep back	No	No	Yes	No
refuse	Yes	No	Yes	No

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

Other hypernyms of keep back include deny.

keep back (noun)	refuse (noun)
	food that is discarded (as from a kitchen)

keep back (verb)	refuse (verb)
prevent the action or expression of	show unwillingness towards
hold back; refuse to hand over or share	not accept as true
secure and keep for possible future use or application	refuse to let have
	refuse entrance or membership
	elude, especially in a baffling way
	resist immunologically the introduction of some foreign tissue or organ