Definitions of antecedent:

• noun:   the referent of an anaphor; a phrase or clause that is referred to by an anaphoric pronoun
• noun:   a preceding occurrence or cause or event
• noun:   anything that precedes something similar in time

  Example: "Phrenology was an antecedent of modern neuroscience"

• noun:   someone from whom you are descended (but usually more remote than a grandparent)
• adjective:   preceding in time or order