A superior lord, to whom fealty is due; a feudal lord; a lord paramount.
In the Middle Ages, the suzerain was a person who owned the right over another (called the vassal) who promised to fight and be loyal in return for being given land to live on.
A feudal overlord. The king as suzerain was the highest feudal lord in the kingdom. (Waugh, Scott. England in the Reign of Edward III, 238)