A technical term in grammar for the word or phrase to which a relative pronoun refers. In a sentence like "She couldn't stand opera, which always sounded like shrieking," the relative pronoun which stands in for the word opera, so opera is the antecedent. In a sentence like "He couldn't say the word titillate without giggling, which always got him in trouble," the word which refers back not to any individual word, but to the whole preceding clause ("He couldn't say the word titillate without giggling") — the whole thing is the antecedent.
By the way, it's pronounced ant-uh-SEE-dent. (Lynch)
