late 14c. in grammar ("noun to which a pronoun refers") and in logic ("if A is, then B is;" A is the antecedent, B the consequent), from Old French antecedent (14c.) or directly from Latin antecedentem (nominative antecedens), noun use of present participle of antecedere "go before, precede," from ante "before" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before") + cedere "to yield" (from PIE root *ked- "to go, yield").
Hence "an event upon which another follows" (1610s). As an adjective in English from c. 1400. Related: Antecedently.