keep back vs retain

keep back and retain both are verbs.

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

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

keep back and retain: secure and keep for possible future use or application

Other synonyms of keep back include hold, hold back.

keep back (verb)	retain (verb)
prevent the action or expression of	keep in one's mind
hold back; refuse to hand over or share	secure and keep for possible future use or application
secure and keep for possible future use or application	allow to remain in a place or position or maintain a property or feature
	hold back within