Part of speech: Adjective
clearly defined or formulated
Example: the plain and unequivocal language of the laws"- R.B.Taney
Part of speech: Adjective
supplying or being a final or conclusive settlement
Example: a definitive verdict; a determinate answer to the problem
Authoritative, Unequivocal, Classic, Classical, Determinate
The word "definitive" comes from Middle French définitif.
The Norman Conquest of 1066 brought thousands of French words into English overnight.