WordNet (r) 3.0 (2006):

seigneur
    n 1: a man of rank in the ancient regime [syn: feudal lord,
         seigneur, seignior]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "seigneur":
   Brahman, archduke, aristocrat, armiger, baron, baronet, blue blood,
   boss, bwana, chef, chief, church dignitary, count, daimio, duke,
   earl, ecclesiarch, elder, employer, esquire, gentleman, goodman,
   grand duke, grandee, guru, hidalgo, husband, lace-curtain, laird,
   landgrave, liege, liege lord, lord, lord paramount, lordling,
   magnate, magnifico, margrave, marquis, master, noble, nobleman,
   optimate, overlord, padrone, palsgrave, paramount, paterfamilias,
   patriarch, patrician, patron, peer, rabbi, sahib, seignior,
   silk-stocking, squire, starets, swell, teacher, thoroughbred,
   upper-cruster, viscount, waldgrave