withhold vs keep back

withhold and keep back both are verbs.

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

As verbs, withhold and keep back are synonyms defined as:

withhold (verb)	keep back (verb)
hold back; refuse to hand over or share	prevent the action or expression of
retain and refrain from disbursing; of payments	hold back; refuse to hand over or share
	secure and keep for possible future use or application