In grammar, an antecedent is an expression (word, phrase, clause, etc.) that gives its meaning to a pro-form (pronoun, pro-verb, pro-adverb, etc.).A proform takes its meaning from its antecedent, e.g. Susan arrived late because traffic held her up.rom Wikipedia, the free encyclopedia. In grammar, an antecedent is an expression (word, phrase, clause, etc.) that gives its meaning to a pro-form (pronoun, pro-verb, pro-adverb, etc.). A proform takes its meaning from its antecedent, e.g. Susan arrived late because traffic held her up.