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)

Moby Thesaurus II by Grady Ward, 1.0:

312 Moby Thesaurus words for "spasm":
   Jacksonian epilepsy, Rolandic epilepsy, abdominal epilepsy,
   abscess, access, ache, aching, acquired epilepsy,
   activated epilepsy, acute pain, ado, affect epilepsy, agitation,
   ague, akinetic epilepsy, amok, anemia, ankylosis, anoxia, apnea,
   apoplexy, arrest, asphyxiation, asthma, ataxia, atrophy, attack,
   autonomic epilepsy, backache, bite, blaze, bleeding, blennorhea,
   blockage, bloodless revolution, blow, boring pain, bother,
   botheration, bouleversement, breakdown, breakup, bumpiness, burst,
   bustle, cachexia, cachexy, cardiac epilepsy, cataclysm,
   catastrophe, charley horse, chill, chills, chorea, clean slate,
   clean sweep, climax, clonic spasm, clonus, cold shivers, colic,
   commotion, computer revolution, constipation, convulsion,
   cortical epilepsy, coughing, counterrevolution, cramp, cramps,
   crick, cursive epilepsy, cut, cyanosis, cyclone, darting pain,
   debacle, diarrhea, diastrophism, disaster, distress,
   diurnal epilepsy, dizziness, dolor, dropsy, dysentery, dyspepsia,
   dyspnea, eclampsia, edema, emaciation, epilepsia,
   epilepsia gravior, epilepsia major, epilepsia minor,
   epilepsia mitior, epilepsia nutans, epilepsia tarda, epilepsy,
   epitasis, eruption, explosion, fainting, falling sickness, fatigue,
   feery-fary, ferment, fever, fibrillation, fidgetiness, fit,
   fits and starts, flap, flare-up, flurry, fluster, flutter,
   flutteriness, flux, focal epilepsy, frenzy, fulgurant pain, furor,
   fury, fuss, fussiness, gale, girdle pain, gnawing, grand mal,
   grief, grip, griping, growth, gust, haute mal, hemorrhage,
   high blood pressure, hitch, hubbub, hullabaloo, hurricane, hurt,
   hydrops, hypertension, hypotension, hysterical epilepsy, icterus,
   ictus, indigestion, inflammation, injury, insomnia, irruption,
   itching, jactation, jactitation, jaundice, jerkiness, joltiness,
   jumping pain, kink, labored breathing, lancinating pain,
   larval epilepsy, laryngeal epilepsy, laryngospasm, latent epilepsy,
   lesion, lockjaw, low blood pressure, lumbago, maelstrom, marasmus,
   matutinal epilepsy, menstrual epilepsy, murderous insanity,
   musicogenic epilepsy, myoclonous epilepsy, nasal discharge,
   nasty blow, nausea, necrosis, nip, nocturnal epilepsy, occlusion,
   orgasm, outbreak, outburst, overthrow, overturn, pain,
   palace revolution, palsy, pang, paralysis, paroxysm, passion,
   petit mal, physiologic epilepsy, pinch, pother, prick, pruritus,
   psychic epilepsy, psychokinesia, psychomotor epilepsy, quake,
   quaking, quavering, quivering, radical change, rage, rash,
   reflex epilepsy, restlessness, revolt, revolution,
   revolutionary war, revulsion, rheum, rotatoria, sclerosis,
   scramble, seizure, sensory epilepsy, serial epilepsy,
   sexual climax, shakes, shaking, sharp pain, shivering, shivers,
   shock, shoot, shooting, shooting pain, shuddering, skin eruption,
   sneezing, sore, sore spot, spasms, spell, spurt, stab,
   stabbing pain, stew, stir, stitch, stoppage, storm, stress,
   stress of life, striking alteration, stroke, subversion,
   succussion, suffering, sweat, sweeping change, swirl, tabes,
   tabula rasa, tachycardia, tardy epilepsy, technological revolution,
   temblor, tempest, tender spot, tetanus, tetany, thrill, throe,
   throes, thromboembolism, thrombosis, tidal wave, to-do,
   tonic epilepsy, tonic spasm, tormen, tornado, torsion spasm,
   total change, transilience, traumatic epilepsy, trembling,
   tremulousness, trismus, tsunami, tumor, tumult, tweak, twinge,
   twitch, ucinate epilepsy, unquiet, upheaval, upset, upset stomach,
   vertigo, vibration, violent change, visitation, vomiting, vortex,
   wasting, whirl, whirlwind, wound, wrench