a preceding circumstance, event, object, style, phenomenon, etc.
antecedents. ancestors. the history, events, characteristics, etc., of one's earlier life: Little is known about his birth and antecedents.
Grammar. a word, phrase, or clause, usually a substantive, that is replaced by a pronoun or other substitute later, or occasionally earlier, in the same or in another, usually subsequent, sentence. In Jane lost a glove and she can't find it, Jane is the antecedent of she and glove is the antecedent of it.
Mathematics. the first term of a ratio; the first or third term of a proportion. the first of two vectors in a dyad.