Megatsunami definition

From the Greek prefix mega- "large", plus Japanese 津波 / 津浪 (つなみ, tsunami), "harbour wave"

A megatsunami is a term used by the popular media to describe very large tsunamis, which are very large and destructive waves that are generally caused by a tremendous disturbance in the ocean floor. The term megatsunami is used informally for tsunamis with wave heights of 40 m or greater.