\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}.