The Collaborative International Dictionary of English v.0.48:

Convulsion \Con*vul"sion\, n. [L. convulsio: cf. F. convulsion.]
   1. (Med.) An unnatural, violent, and unvoluntary contraction
      of the muscular parts of an animal body.
      [1913 Webster]

   2. Any violent and irregular motion or agitation; a violent
      shaking; a tumult; a commotion.
      [1913 Webster]

            Those two massy pillars,
            With horrible convulsion, to and fro
            He tugged, he shook, till down they came. --Milton.
      [1913 Webster]

            Times of violence and convulsion.     --Ames.

   Syn: Agitation; commotion; tumult; disturbance.
        [1913 Webster]

WordNet (r) 3.0 (2006):

convulsion
    n 1: a sudden uncontrollable attack; "a paroxysm of giggling";
         "a fit of coughing"; "convulsions of laughter" [syn:
         paroxysm, fit, convulsion]
    2: violent uncontrollable contractions of muscles
    3: a violent disturbance; "the convulsions of the stock market"
       [syn: convulsion, turmoil, upheaval]
    4: a physical disturbance such as an earthquake or upheaval

Moby Thesaurus II by Grady Ward, 1.0:

277 Moby Thesaurus words for "convulsion":
   Homeric laughter, Jacksonian epilepsy, Rolandic epilepsy,
   abdominal epilepsy, abscess, access, acquired epilepsy,
   activated epilepsy, affect epilepsy, ague, akinetic epilepsy, amok,
   anemia, ankylosis, anoxia, apnea, apoplexy, arrest, asphyxiation,
   asthma, ataxia, atrophy, attack, autonomic epilepsy, backache,
   belly laugh, blaze, bleeding, blennorhea, blockage,
   bloodless revolution, boff, boffola, bouleversement, breakdown,
   breakup, burst, burst of laughter, cachexia, cachexy, cachinnation,
   cackle, cardiac epilepsy, cat fit, cataclysm, catastrophe, chill,
   chills, chortle, chuckle, clamor, clean slate, clean sweep, climax,
   clonic spasm, clonus, colic, computer revolution, conniption,
   conniption fit, constipation, cortical epilepsy, coughing,
   counterrevolution, cramp, crow, cursive epilepsy, cyanosis,
   cyclone, debacle, derangement, diarrhea, diastrophism,
   disarrangement, disaster, discomposure, dislocation, disorder,
   disorganization, disturbance, diurnal epilepsy, dizziness,
   downfall, dropsy, duck fit, dysentery, dyspepsia, dyspnea,
   eclampsia, edema, emaciation, epilepsia, epilepsia gravior,
   epilepsia major, epilepsia minor, epilepsia mitior,
   epilepsia nutans, epilepsia tarda, epilepsy, epitasis, eruption,
   explosion, fainting, fall, falling sickness, fatigue, ferment,
   fever, fibrillation, fit, fit of anger, fit of laughter,
   fit of temper, flare-up, flux, focal epilepsy, frenzy, furor, fury,
   gale, gales of laughter, giggle, grand mal, grip, growth, guffaw,
   gust, ha-ha, haute mal, hearty laugh, hee-haw, hee-hee, hemorrhage,
   high blood pressure, hilarity, ho-ho, horselaugh, hurricane,
   hydrops, hypertension, hypotension, hysterical epilepsy, icterus,
   ictus, indigestion, inflammation, insanity, insomnia, irruption,
   itching, jaundice, labored breathing, larval epilepsy,
   laryngeal epilepsy, laryngospasm, latent epilepsy, laugh, laughing,
   laughter, lockjaw, low blood pressure, lumbago, marasmus,
   matutinal epilepsy, menstrual epilepsy, misarrangement,
   murderous insanity, musicogenic epilepsy, myoclonous epilepsy,
   nasal discharge, nausea, necrosis, nocturnal epilepsy, occlusion,
   orgasm, outbreak, outburst, outburst of laughter, outcry,
   overthrow, overturn, pain, palace revolution, paralysis, paroxysm,
   peal of laughter, perturbation, petit mal, physiologic epilepsy,
   prostration, pruritus, psychic epilepsy, psychokinesia,
   psychomotor epilepsy, quake, quaking, radical change, rage, rash,
   reflex epilepsy, revolt, revolution, revolutionary war, revulsion,
   rheum, risibility, roar of laughter, rocking, rotatoria, sabotage,
   sclerosis, seizure, sensory epilepsy, serial epilepsy,
   sexual climax, shaking, shock, shout, shout of laughter, shriek,
   shuffling, skin eruption, sneezing, snicker, snigger, snort, sore,
   spasm, stoppage, storm, striking alteration, stroke, subversion,
   sweeping change, tabes, tabula rasa, tachycardia, tantrum,
   tardy epilepsy, technological revolution, tee-hee, temblor,
   temper tantrum, tempest, tetanus, tetany, throes, thromboembolism,
   thrombosis, tidal wave, titter, tonic epilepsy, tonic spasm,
   tornado, torsion spasm, total change, tottering, transilience,
   traumatic epilepsy, trembling, trismus, tsunami, tumor, tumult,
   ucinate epilepsy, upheaval, upset, upset stomach, upturn, vertigo,
   violent change, visitation, vomiting, wasting, whirlwind, yuck,
   yuk-yuk