Idioms: Deep Six

What is the origin of the idiom “Deep Six,” (to bury or be dead).

  1. A grave commonly measures 3 feet wide by six feet deep.
  1. The six refers to the sixth level of sleep, the deepest level.
  1. In the original game of high stakes billards the six ball was the death ball, and if you sank the ball on the first shot, the opponent had the choice to kill you.
  1. Deep six was a nautical expression referring to the depth of shallow water; deep six referred to a depth of sixth fathoms. Something buried at a depth of deep six would likely remain submerged even a low tide.