treaty (n.)youdaoicibaDictYouDict[treaty 词源字典]
late 14c., "treatment, discussion," from Anglo-French treté, Old French traitié "assembly, agreement, dealings," from Latin tractatus "discussion, handling, management," from tractare "to handle, manage" (see treat (v.)). Sense of "contract or league between nations or sovereigns" is first recorded early 15c.[treaty etymology, treaty origin, 英语词源]