A typhoon is a weather phenomenon, while a tsunami is not.
Once a weather disturbance occurs in the Northwest Pacific area, it is called a typhoon. It is a low pressure system of tropical origin containing organized thunderstorm activity that produces sustained winds of at least 74 mph.
On the other hand, tsunami is a high energy undersea wave, which is usually caused by an undersea earthquake, volcanic explosion or landslide.
In the news, some compared Super Typhoon Haiyan devastation to the mayhem caused by the 2004 Indian Ocean tsunami, which resulted from a magnitude-9.1 earthquake that struck west of the island of Sumatra on Dec. 26 of that year. Scenes of walls of water moving across coastal villages seemed to connect the two events in people's minds. Read more at Mother Nature Network.