rebuff vs rejection

rebuff and rejection both are nouns.

Word	Noun	Adjective	Verb	Adverb
rebuff	Yes	No	Yes	No
rejection	Yes	No	No	No

As nouns, rejection is a hypernym of rebuff; that is, rejection is a word with a broader meaning than rebuff:

rebuff (noun)	rejection (noun)
a deliberate discourteous act (usually as an expression of anger or disapproval)	the act of rejecting something
an instance of driving away or warding off	the speech act of rejecting
	(medicine) an immunological response that refuses to accept substances or organisms that are recognized as foreign
	the state of being rejected

rebuff (verb)	rejection (verb)
reject outright and bluntly
force or drive back