Definition of sigmoid in US English:



  • 1Curved like the uncial sigma (C); crescent-shaped.

    • ‘Usually, a time course of plant growth follows a sigmoid curve, which can be described by a logistic function.’
    • ‘The main body of the element comprises a longitudinal bony buttress that supports a very slight sigmoid row containing a minimum of five shallow tooth sockets.’
    • ‘To isolate deviations from typical tree growth, we developed a model based on the amount of shoot elongation, which over equal time intervals approximates a sigmoid curve.’
    • ‘The growth curve of the fruit of Marisol clementine fitted a single sigmoid curve well.’
    • ‘Fruit development was described by an approximately sigmoid growth pattern based on fresh weight, irrespective of cultivar.’
  • 2S-shaped.

    • ‘‘The river flows in long sigmoid Curves,’ he wrote, ‘through an alluvial valley of no great width.’’
    • ‘First, the cumulative adoption of an innovation over time follows an S-shaped or sigmoid curve.’
    • ‘A series of unsuccessful attempts at scheduling surgery for her sigmoid colectomy followed because of complications with her neutrophil count and hospitalization for new onset atrial fibrillation.’


  • short for sigmoid colon
    • ‘Although sigmoid volvulus can resolve spontaneously, nonoperative management begins with fluid resuscitation and antibiotics, followed by barium enema detorsion of the sigmoid.’
    • ‘The most frequently involved site is the sigmoid.’
    • ‘An enema shows a normal sized rectum and small caliber sigmoid and descending colon with a transition zone in colonic caliber occurring at the level of the splenic flexure.’
    • ‘The sigmoid may lie in the abdomen just inferior to the splenic flexure of the transverse colon, or in the right iliac fossa.’


Late 17th century: from Greek sigmoeidēs, from sigma (see sigma).