Definition from Wiktionary, the free dictionary
sigmoid (not comparable)
- (geometry) Curved in two directions, like the letter "S", or the Greek ς (sigma).
- (geometry, archaic) Semi-circular, like the lunar sigma (similar to English C).
- (anatomy) Relating to the sigmoid flexure of the large intestine.
Derived terms 
- sigmoid artery
- sigmoid colon
- sigmoid flexure
- sigmoid fossa
- sigmoid groove
- sigmoid sinus
- sigmoid valve
- sigmoid function
in geometry: curved in two directions
in geometry: semi-circular
in anatomy: relating to the sigmoid flexure of the large intestine
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sigmoid (plural sigmoids)
in mathematics: function having a graph whose shape is sigmoid