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]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "prognostic":
   apocalyptic, augural, auguring, augury, boding, divinatory,
   fatidic, forecasting, forerunning, foreseeing, foreshadowing,
   foreshowing, foretelling, foretokening, forewarning,
   fortunetelling, haruspical, heavy with meaning, indicative,
   intuitive, mantic, meaningful, monitory, omen, oracular, portent,
   precursive, precursory, predictional, predictive, predictory,
   prefigurative, prefiguring, preindicative, premonitory, presage,
   presageful, presaging, presignificative, presignifying,
   prognosticative, prophetic, sibyllic, sibylline, significant,
   vaticinal, vaticinatory, warning, weather-wise