Definition of Sigmoid

Sigmoid: In human anatomy, the lower colon (the lower portion of the large bowel). "Sigmoid" is short for "sigmoid colon."

The word "sigmoid" came from the Greek letter "sigma" which is shaped like a C. It also means curved in two directions like the letter S. A sigmoid curve is an S-shaped curve.

The sigmoid flexure of the colon is the point where it makes the turn from transverse to descending colon. Sigmoidoscopy is a procedure in which a viewing tube (a sigmoidoscope) is inserted up into the sigmoid colon. The term "rectosigmoid" refers to both the rectum and the sigmoid colon above it.