desertion vs rejection

desertion and rejection both are nouns.

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

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

desertion (noun)	rejection (noun)
withdrawing support or help despite allegiance or responsibility	the act of rejecting something
the act of giving something up	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