walk the plank
On an early naval vessel or pirate ship: to be forced to walk off the end of a gangplank (a plank of wood extending outwards from the side of the vessel) and plunge into the ocean and drown, used as a method of killing.
Walking the Plank. A mode of deſtroying devoted perſons or officers in a mutiny on ſhip-board, by blindfolding them, and obliging them to walk on a plank laid over the ſhip's ſide;