[syn: capstone, copestone, coping stone, stretcher]
The Collaborative International Dictionary of English v.0.48:
Capstone \Cap"stone`\, n. (Paleon.)
   A fossil echinus of the genus Cannulus; -- so called from
   its supposed resemblance to a cap.
   [1913 Webster] Capsular
WordNet (r) 3.0 (2006):
capstone
    n 1: a final touch; a crowning achievement; a culmination [syn:
         finishing touch, capstone, copestone]
    2: a stone that forms the top of wall or building [syn:
       capstone, copestone, coping stone, stretcher]