keep back vs reserve

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

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

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

Other hyponyms of keep back include block, freeze, immobilise, immobilize, keep to oneself, deny, immobilise, immobilize, deprive.

keep back (noun)	reserve (noun)
	the trait of being uncommunicative; not volunteering anything more than necessary
	formality and propriety of manner
	armed forces that are not on active duty but can be called in an emergency
	a district that is reserved for particular purpose
	an athlete who plays only when a starter on the team is replaced
	something kept back or saved for future use or a special purpose
	(medicine) potential capacity to respond in order to maintain vital functions

keep back (verb)	reserve (verb)
prevent the action or expression of	give or assign a resource to a particular person or cause
hold back; refuse to hand over or share	obtain or arrange (for oneself) in advance
secure and keep for possible future use or application	hold back or set aside, especially for future use or contingency
	arrange for and reserve (something for someone else) in advance