A typhoon is a tropical storm of cyclonic force and peculiar violence occurring in the Western Pacific and the China Sea.
A cyclone is a system of wind circulating about the center of a relatively low barometric pressure advancing clockwise rotation in the southern hemisphere and counterclockwise in the northern, while a tornado is a whirling wind of exceptional violence occuring in the Tropical Atlantic and Africa, usually associated with thunderstorms and accompanied by a pendulous funnel-shaped cloud marking its path with greatest destruction.
A hurricane, in the otherhand is a tropical cyclone originating from the West Indies with a force of the 12th or highest degree moving at the speed of more than 75 miles an hour.
Source(s):
The New International Webster's Comprehensive Dictionary
http://answers.yahoo.com/question/index?qid=20080508051036AAAYTbJ"typhoon" is of chinese/japanese derivation: "tai" (great/strong) + "fu" (wind)