[Fred Nerks]

...TSUNAMI : a great sea wave produced especially by submarine earth movement or volcanic eruption : tidal wave

Right. Obviously NOT caused by a long period of heavy torrential rain over a wide area of LAND.

[RowdyFFC]

A tsunami|津波| is a series of water waves (called a tsunami wave train) caused by the displacement of a large volume of a body of water. A very large and destructive wave, generally caused by a tremendous disturbance in water flow. And/or: efinition of TSUNAMI : a great sea wave produced especially by submarine earth movement or volcanic eruption : tidal wave