\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.
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.
{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.