The Collaborative International Dictionary of English v.0.48:

Prognosis \Prog*no"sis\ (pr[o^]g*n[=o]"s[i^]s), n. [L., fr. Gr.
   pro`gnosis, fr. progignw`skein to know beforehand; pro`
   before + gignw`skein to know. See Know.] (Med.)
   The act or art of foretelling the course and termination of a
   disease; also, the outlook afforded by this act of judgment;
   as, the prognosis of hydrophobia is bad.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prognosis
    n 1: a prediction about how something (as the weather) will
         develop [syn: prognosis, forecast]
    2: a prediction of the course of a disease [syn: prognosis,
       prospect, medical prognosis]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "prognosis":
   action, actuarial prediction, apocalypse, award, cast,
   condemnation, consideration, decision, decree, deliverance,
   determination, diagnosis, dictum, doom, finding, foreboding,
   forecast, forecasting, foreshowing, foresight, foretelling,
   guesswork, improbability, omen, order, precedent, prediction,
   prefiguration, prefigurement, prefiguring, presage, presaging,
   presentiment, preshowing, presignifying, prevision, probability,
   prognostic, prognostication, projection, promise, pronouncement,
   prophecy, prophesying, prospectus, resolution, ruling, sentence,
   sign, soothsay, speculation, statistical prediction, symptom,
   vaticination, verdict, weird