late Middle English: from Old French definitif, -ive, from Latin definitivus, from definit- 'set within limits', from the verb definire (see define)
Definitive in the sense ‘decisive, unconditional, final’ is sometimes confused with definite. Definite means ‘clearly defined, precise, having fixed limits,’ but definitive goes further, meaning ‘most complete, satisfying all criteria, most authoritative’: although some critics found a few definite weak spots in the author’s interpretations, his book was nonetheless widely regarded as the definitive history of the war. A definite decision is simply one that has been made clearly and is without doubt, whereas a definitive decision is one that is not only conclusive but also carries the stamp of authority or is a benchmark for the future, as in a Supreme Court ruling. It is a common error to use definitive as though it were a more elegant way of saying definite.