The Collaborative International Dictionary of English v.0.48:

Symptom \Symp"tom\, n. [F. sympt[^o]me, Gr. ? anything that has
   befallen one, a chance, causality, symptom, fr. ? to fall
   together; sy`n with + ? to fall; akin to Skr. pat to fly, to
   fall. See Syn-, and cf. Asymptote, Feather.]
   1. (Med.) Any affection which accompanies disease; a
      perceptible change in the body or its functions, which
      indicates disease, or the kind or phases of disease; as,
      the causes of disease often lie beyond our sight, but we
      learn their nature by the symptoms exhibited.
      [1913 Webster]

            Like the sick man, we are expiring with all sorts of
            good symptoms.                        --Swift.
      [1913 Webster]

   2. A sign or token; that which indicates the existence of
      something else; as, corruption in elections is a symptom
      of the decay of public virtue.
      [1913 Webster]

   Syn: Mark; note; sign; token; indication.
        [1913 Webster] Symptomatic

WordNet (r) 3.0 (2006):

symptom
    n 1: (medicine) any sensation or change in bodily function that
         is experienced by a patient and is associated with a
         particular disease
    2: anything that accompanies X and is regarded as an indication
       of X's existence

Moby Thesaurus II by Grady Ward, 1.0:

184 Moby Thesaurus words for "symptom":
   abnormality, acute disease, affection, affliction, ailment,
   allergic disease, allergy, atrophy, bacterial disease, badge,
   banner, basis for belief, birth defect, blight, body of evidence,
   broad hint, cardiovascular disease, chain of evidence, character,
   characteristic, chronic disease, circulatory disease, clue,
   complaint, complication, condition, congenital defect, cue,
   danger sign, data, datum, defect, deficiency disease, deformity,
   degenerative disease, device, differentia, disability, disease,
   disorder, distemper, documentation, early symptom, earmark,
   endemic, endemic disease, endocrine disease, epidemic disease,
   evidence, exhibit, fact, facts, falling barometer, feature,
   functional disease, fungus disease, gastrointestinal disease,
   gathering clouds, genetic disease, gentle hint, gesture, glimmer,
   glimmering, grounds, grounds for belief, hallmark, handicap,
   hereditary disease, high sign, hint, iatrogenic disease,
   idiosyncrasy, illness, image, implication, index, indicant,
   indication, indicator, indisposition, infectious disease,
   infirmity, inkling, innuendo, insignia, insinuation, intimation,
   item of evidence, keynote, kick, look, malady, malaise,
   manifestation, mark, marker, material grounds, measure, morbidity,
   morbus, muniments, muscular disease, mute witness,
   neurological disease, nod, note, nudge, nutritional disease,
   occupational disease, omen, organic disease, pandemic disease,
   pathological condition, pathology, peculiarity, picture,
   piece of evidence, plant disease, precursor, preliminary sign,
   premises, premonitory sign, premonitory symptom, prodroma,
   prodrome, prognosis, prognostic, prognostication, prompt, proof,
   property, protozoan disease, psychosomatic disease,
   quarantine flag, reason to believe, red flag, red light,
   relevant fact, representation, representative, respiratory disease,
   rockiness, scent, seal, secondary disease, seediness, sickishness,
   sickness, sigil, sign, signal, signature, significant, signs,
   skull and crossbones, spoor, stamp, storm petrel, stormy petrel,
   suggestion, sure sign, suspicion, symptomatology, symptomology,
   symptoms, syndrome, telltale, telltale sign, the pip, thundercloud,
   thunderhead, token, track, trait, urogenital disease,
   virus disease, warning sign, warning signal, wasting disease,
   whisper, wink, worm disease, yellow flag, yellow jack