The Collaborative International Dictionary of English v.0.48:

Shogun \Sho"gun\ (sh[=o]"g[=oo]n), n. [Jap. military general,
   from Chin. tsiang ki["u]n commander in chief.]
   A title originally conferred by the Mikado on the military
   governor of the eastern provinces of Japan. By gradual
   usurpation of power the Shoguns (known to foreigners as
   Tycoons) became finally the virtual rulers of Japan. The
   title was abolished in 1867. [Written variously, Shiogun,
   Shiogoon, etc.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

shogun
    n 1: a hereditary military dictator of Japan; the shoguns ruled
         Japan until the revolution of 1867-68

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "shogun":
   Dalai Lama, Holy Roman Emperor, Inca, Kaiser, ardri, bey, cacique,
   caesar, cham, czar, kaid, khan, mikado, negus, padishah, pendragon,
   pharaoh, rig, sachem, sagamore, shah, sheikh, tenno, tycoon