antecedent vs antecedency

antecedent and antecedency both are nouns.

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

antecedent (noun)	antecedency (noun)
the referent of an anaphor; a phrase or clause that is referred to by an anaphoric pronoun	preceding in time
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

antecedent (adjective)	antecedency (adjective)
preceding in time or order