The Collaborative International Dictionary of English v.0.48:

Prognostic \Prog*nos"tic\, a. [Gr. prognwstiko`n. See
   Prognosis.]
   Indicating something future by signs or symptoms;
   foreshowing; aiding in prognosis; as, the prognostic symptoms
   of a disease; prognostic signs.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Prognostic \Prog*nos"tic\, n. [L. prognosticum, Gr. ?: cf. F.
   pronostic, prognostic. See Prognostic, a.]
   [1913 Webster]
   1. That which prognosticates; a sign by which a future event
      may be known or foretold; an indication; a sign or omen;
      hence, a foretelling; a prediction.
      [1913 Webster]

            That choice would inevitably be considered by the
            country
            as a prognostic of the highest import. --Macaulay.
      [1913 Webster]

   2. (Med.) A sign or symptom indicating the course and
      termination of a disease. --Parr.
      [1913 Webster]

   Syn: Sign; omen; presage; token; indication.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Prognostic \Prog*nos"tic\, v. t.
   To prognosticate. [Obs.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

prognostic
    adj 1: of or relating to prediction; having value for making
           predictions [syn: predictive, prognostic,
           prognosticative]
    n 1: a sign of something about to happen; "he looked for an omen
         before going into battle" [syn: omen, portent,
         presage, prognostic, prognostication, prodigy]