keep back vs restrain

keep back and restrain both are verbs.

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

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

Other synonyms of keep back include hold back, keep.

keep back (verb)	restrain (verb)
prevent the action or expression of	prevent the action or expression of
hold back; refuse to hand over or share	to close within bounds, or otherwise limit or deprive of free movement
secure and keep for possible future use or application	restrict (someone or something) so as to make free movement difficult
	prevent (someone or something) from doing something