tor·sion / ˈtôrshən/ • n. the action of twisting or the state of being twisted, esp. of one end of an object relative to the other. ∎ Math. the extent to which a curve departs from being planar. ∎ Zool. (in a gastropod mollusk) the spontaneous twisting of the visceral hump through 180° during larval development. DERIVATIVES: tor·sion·al / -shənl/ adj. tor·sion·al·ly / -shənl-ē/ adv. tor·sion·less adj.
1. The effect of twisting an object in opposite directions from either end. Torsion tests, using rod-shaped samples, allow stable ductile deformation to be studied up to large strain states.
2. In Gastropoda, the twisting of the body through 180° so that the digestive and nervous systems have a U-shape and the mantle cavity, anus, gills, and two nephridiopores (excretory openings) occupy an anterior position behind the head.