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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Sigmoid \Sig"moid\, Sigmoidal \Sig*moid"al\, a. [Gr. ???; ??? sigma + ??? form, likeness: cf. F. sigmo["i]de.]

Curved in two directions, like the letter S, or the Greek [sigmat].

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.

Source: Webster's Revised Unabridged Dictionary (1913)