The Collaborative International Dictionary of English v.0.48:

Spasm \Spasm\, n. [F. spasme, L. spasmus, Gr. ?, from ?, ?, to
   draw, to cause convulsion. Cf. Span, v. t.]
   1. (Med.) An involuntary and unnatural contraction of one or
      more muscles or muscular fibers.
      [1913 Webster]

   Note: Spasm are usually either clonic or tonic. In clonic
         spasm, the muscles or muscular fibers contract and
         relax alternately in very quick succession. In tonic
         spasm, the contraction is steady and uniform, and
         continues for a comparatively long time, as in tetanus.
         [1913 Webster]

   2. A sudden, violent, and temporary effort or emotion; as, a
      spasm of repentance.
      [1913 Webster]

   Cynic spasm (Med.) See under Cynic.

   Spasm of the chest. See Angina pectoris, under Angina.
      [1913 Webster]

WordNet (r) 3.0 (2006):

spasm
    n 1: a painful and involuntary muscular contraction [syn:
         spasm, cramp, muscle spasm]
    2: (pathology) sudden constriction of a hollow organ (as a blood
       vessel)