Source : Webster's Revised Unabridged Dictionary (1913)

Semilunar \Sem`i*lu"nar\, a.
   Shaped like a half moon.

   {Semilunar bone} (Anat.), a bone of the carpus; the lunar.
      See {Lunar}, n.

   {Semilunar}, or {Sigmoid}, {valves} (Anat.), the valves at
      the beginning of the aorta and of the pulmonary artery
      which prevent the blood from flowing back into the
      ventricle.