1922, Virginia Woolf, Jacob's Room Chapter 2True, there's no harm in crying for one's husband, and the tombstone, though plain, was a solid piece of work, and on summer's days when the widow brought her boys to stand there one felt kindly towards her.
(mathematics) The symbol "∎" marking the end of a proof.
(surfing) For a surfboard to stand upright half-submerged in the water (like a tombstone, above) because the surfer is underwater with his or her legrope pulled tight. Often this indicates a surfer in difficulty, either held down by the power of a wave or unconscious and unable to get to the surface.
2005, Bruce Jenkins, Surfer magazine, (referring to Kelly Slater) http://surfermag.com/features/events/mav05/:Before the contest even started, Slater went down hard in a warmup session. He took a two-wave hold-down in the semifinals, his board tombstoning eerily for all to see, ...
