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