to walk the plank

GNU Webster's 1913

1. n. to walk along a plank laid across the bulwark of a ship, until one overbalances it and falls into the sea; -- a method of disposing of captives practiced by pirates.
2. v. to walk off the plank into the water and be drowned; -- an expression derived from the practice of pirates who extended a plank from the side of a ship, and compelled those whom they would drown to walk off into the water; figuratively, to vacate an office by compulsion.