preexisting vs antecedent

preexisting is not a noun while antecedent is a noun.

Word	Noun	Adjective	Verb	Adverb
preexisting	No	Yes	No	No
antecedent	Yes	Yes	No	No

preexisting (noun)	antecedent (noun)
	the referent of an anaphor; a phrase or clause that is referred to by an anaphoric pronoun
	a preceding occurrence or cause or event
	someone from whom you are descended (but usually more remote than a grandparent)
	anything that precedes something similar in time

preexisting (adjective)	antecedent (adjective)
existing previously or before something	preceding in time or order