pass up vs reject

pass up is not a noun while reject is a noun.

Word	Noun	Adjective	Verb	Adverb
pass up	No	No	Yes	No
reject	Yes	No	Yes	No

As verbs, pass up and reject are synonyms defined as:

Other synonyms of pass up include decline, refuse, turn down.

pass up (noun)	reject (noun)
	the person or thing that is rejected or set aside as inferior in quality

pass up (verb)	reject (verb)
fail to acknowledge	not accept something given or offered
not accept as true	dismiss from consideration or a contest
	deem wrong or inappropriate
	reject with contempt
	not accept as true
	refuse entrance or membership
	resist immunologically the introduction of some foreign tissue or organ