The Collaborative International Dictionary of English v.0.48:

Torsion \Tor"sion\, n. [F., fr. LL. torsio, fr. L. torquere,
   tortum, to twist. See Torture.]
   1. The act of turning or twisting, or the state of being
      twisted; the twisting or wrenching of a body by the
      exertion of a lateral force tending to turn one end or
      part of it about a longitudinal axis, while the other is
      held fast or turned in the opposite direction.
      [1913 Webster]

   2. (Mech.) That force with which a thread, wire, or rod of
      any material, returns, or tends to return, to a state of
      rest after it has been twisted; torsibility.
      [1913 Webster]

   Angle of torsion (of a curve) (Geom.), the indefinitely
      small angle between two consecutive osculating planes of a
      curve of double curvature.

   Moment of torsion (Mech.) the moment of a pair of equal and
      opposite couples which tend to twist a body.

   Torsion balance (Physics.), an instrument for estimating
      very minute forces, as electric or magnetic attractions
      and repulsions, by the torsion of a very slender wire or
      fiber having at its lower extremity a horizontal bar or
      needle, upon which the forces act.

   Torsion scale, a scale for weighing in which the fulcra of
      the levers or beams are strained wires or strips acting by
      torsion.
      [1913 Webster]

WordNet (r) 3.0 (2006):

torsion
    n 1: a tortuous and twisted shape or position; "they built a
         tree house in the tortuosities of its boughs"; "the acrobat
         performed incredible contortions" [syn: tortuosity,
         tortuousness, torsion, contortion, crookedness]
    2: a twisting force [syn: torsion, torque]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "torsion":
   ambages, anamorphism, anamorphosis, anfractuosity, asymmetry,
   buckle, circuitousness, circumambages, circumbendibus,
   circumlocution, circumvolution, contortion, convolution, crinkle,
   crinkling, crookedness, deflection, deflexure, detorsion,
   deviation, diffraction, diffusion, dispersion, disproportion,
   distortion, flection, flexuosity, flexuousness, flexure, gnarl,
   imbalance, intorsion, involution, irregularity, knot, lopsidedness,
   meander, meandering, quirk, refraction, rivulation, scatter, screw,
   sinuation, sinuosity, sinuousness, skewness, slinkiness, snakiness,
   stress, torque, tortility, tortuosity, tortuousness, turn, turning,
   twist, twisting, undulation, unsymmetry, warp, wave, waving,
   winding, wrench, wrest, wring