The Collaborative International Dictionary of English v.0.48:

Tycoon \Ty*coon"\ (t[-i]`k[=oo]n"), n. [Chinese tai-kun great
   prince.]
   The title by which the shogun, or former commander in chief
   of the Japanese army, was known to foreigners.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tycoon
    n 1: a very wealthy or powerful businessman; "an oil baron"
         [syn: baron, big businessman, business leader,
         king, magnate, mogul, power, top executive,
         tycoon]