The Oxford Thesaurus An A-Z Dictionary of Synonyms - definitiveadj.

1) decisive, final, conclusive, ultimate: My definitive answer will be given tomorrow. 2) thorough, through and through, exhaustive, ultimate, consummate, complete, authoritative, reliable: She has written the definitive work on the axolotl. 3 clarifying, unambiguous, categorical, absolute, unqualified, accurate, exact, precise: We expect a definitive statement from the union regarding their claims.