refuse vs keep back

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

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

As verbs, keep back is a hyponym of refuse; that is, keep back is a word with a more specific, narrower meaning than refuse:

Other hyponyms of refuse include withhold.

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

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