copestone (plural copestones)

1. capstone
   • 1851 November 13, Herman Melville, chapter 2, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley, OCLC 57395299 ↗:

     The universe is finished; the copestone is on, and the chips were carted off a million years ago.

   • 1851, Herman Melville, Moby Dick, chapter 32

     For small erections may be finished by their first architects; grand ones, true ones, ever leave the copestone to posterity.