Merriam-Webster Collegiate Dictionary - suzerain

 noun  Etymology: French, from Middle French souserain, from sus up (from Latin sursum, from sub- up + versum -ward, from neuter of versus, past participle of vertere to turn) + -erain (as in soverain sovereign) — more at sub-, worth  Date: 1807  1. a superior feudal lord to whom fealty is due ; overlord  2. a dominant state controlling the foreign relations of a vassal state but allowing it sovereign authority in its internal affairs