A surfing type of wave that is growing in size as you approach it. The bansai wave peaks and crashes on a surfers board or boat at the exact time to cause maximum damage and disorientation.
Bansai Wave is also known as a Suicide wave.
"Jesus John, dont paddle out yet, thats a bansai wave building out there."
"Bloody hell, i thought i was going to make that but just as i got there i realised it was a bansai wave. My head hurts now!"