The Collaborative International Dictionary of English v.0.48:

Tetanus \Tet"a*nus\, n. [L., fr. Gr. ?, fr. ? stretched, ? to
   stretch.]
   1. (Med.) A painful and usually fatal disease, resulting
      generally from a wound, and having as its principal
      symptom persistent spasm of the voluntary muscles. When
      the muscles of the lower jaw are affected, it is called
      locked-jaw, or lickjaw, and it takes various names
      from the various incurvations of the body resulting from
      the spasm.
      [1913 Webster]

   2. (Physiol.) That condition of a muscle in which it is in a
      state of continued vibratory contraction, as when
      stimulated by a series of induction shocks.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tetanus
    n 1: an acute and serious infection of the central nervous
         system caused by bacterial infection of open wounds; spasms
         of the jaw and laryngeal muscles may occur during the late
         stages [syn: tetanus, lockjaw]
    2: a sustained muscular contraction resulting from a rapid
       series of nerve impulses

Moby Thesaurus II by Grady Ward, 1.0:

200 Moby Thesaurus words for "tetanus":
   African lethargy, Asiatic cholera, Chagres fever, German measles,
   Haverhill fever, Jacksonian epilepsy, Rolandic epilepsy,
   abdominal epilepsy, access, acquired epilepsy, activated epilepsy,
   acute articular rheumatism, affect epilepsy, ague,
   akinetic epilepsy, alkali disease, amebiasis, amebic dysentery,
   anthrax, apoplexy, arrest, attack, autonomic epilepsy,
   bacillary dysentery, bastard measles, black death, black fever,
   blackwater fever, blockage, breakbone fever, brucellosis,
   bubonic plague, cachectic fever, cardiac epilepsy,
   cerebral rheumatism, chicken pox, cholera, clonic spasm, clonus,
   convulsion, cortical epilepsy, cowpox, cramp, cursive epilepsy,
   dandy fever, deer fly fever, dengue, dengue fever, diphtheria,
   diurnal epilepsy, dumdum fever, dysentery, eclampsia,
   elephantiasis, encephalitis lethargica, enteric fever, epilepsia,
   epilepsia gravior, epilepsia major, epilepsia minor,
   epilepsia mitior, epilepsia nutans, epilepsia tarda, epilepsy,
   erysipelas, falling sickness, famine fever, fit, five-day fever,
   flu, focal epilepsy, frambesia, frenzy, glandular fever, grand mal,
   grippe, hansenosis, haute mal, hepatitis, herpes, herpes simplex,
   herpes zoster, histoplasmosis, hookworm, hydrophobia,
   hysterical epilepsy, ictus, infantile paralysis,
   infectious mononucleosis, inflammatory rheumatism, influenza,
   jail fever, jungle rot, kala azar, kissing disease,
   larval epilepsy, laryngeal epilepsy, laryngospasm, latent epilepsy,
   lepra, leprosy, leptospirosis, loa loa, loaiasis, lockjaw, madness,
   malaria, malarial fever, marsh fever, matutinal epilepsy, measles,
   meningitis, menstrual epilepsy, milzbrand, mumps,
   musicogenic epilepsy, myoclonous epilepsy, nocturnal epilepsy,
   occlusion, ornithosis, osteomyelitis, paratyphoid fever, parotitis,
   paroxysm, parrot fever, pertussis, petit mal, physiologic epilepsy,
   pneumonia, polio, poliomyelitis, polyarthritis rheumatism, ponos,
   psittacosis, psychic epilepsy, psychomotor epilepsy, rabbit fever,
   rabies, rat-bite fever, reflex epilepsy, relapsing fever,
   rheumatic fever, rickettsialpox, ringworm, rotatoria, rubella,
   rubeola, scarlatina, scarlet fever, schistosomiasis, seizure,
   sensory epilepsy, septic sore throat, serial epilepsy, shingles,
   sleeping sickness, sleepy sickness, smallpox, snail fever, spasm,
   splenic fever, spotted fever, stoppage, strep throat, stroke,
   swamp fever, tardy epilepsy, tetany, throes, thromboembolism,
   thrombosis, thrush, tinea, tonic epilepsy, tonic spasm,
   torsion spasm, traumatic epilepsy, trench fever, trench mouth,
   trismus, tuberculosis, tularemia, typhoid, typhoid fever, typhus,
   typhus fever, ucinate epilepsy, undulant fever, vaccinia,
   varicella, variola, venereal disease, viral dysentery, visitation,
   whooping cough, yaws, yellow fever, yellow jack, zona, zoster