Sigmoid

{ Sig"moid (?), Sig*moid"al (?), } a. [Gr. ???; ??? sigma + ??? form, likeness: cf. F. sigmoïde.] Curved in two directions, like the letter S, or the Greek σ.

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.