The Collaborative International Dictionary of English v.0.48:

Semilunar \Sem`i*lu"nar\, a.
   Shaped like a half moon.
   [1913 Webster]

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

   Semilunar valves, 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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sigmoid \Sig"moid\, Sigmoidal \Sig*moid"al\, a. [Gr. ???; ???
   sigma + e'i^dos form, likeness: cf. F. sigmo["i]de.]
   Curved in two directions, like the letter S, or the Greek
   [sigmat].
   [1913 Webster]

   Sigmoid flexure (Anat.), the last curve of the colon before
      it terminates in the rectum. See Illust. under
      Digestive.

   Sigmoid valves. (Anat.) See Semilunar valves, under
      Semilunar.
      [1913 Webster]