Noun

1. A headstone marking the person's grave.
2. The symbol "" (Unicode U+220E, "END OF PROOF") marking the end of a proof.

Verb

1. 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,