The Collaborative International Dictionary of English v.0.48:

Predictor \Pre*dict"or\, n.
   One who predicts; a foreteller.
   [1913 Webster]

WordNet (r) 3.0 (2006):

predictor
    n 1: someone who makes predictions of the future (usually on the
         basis of special knowledge) [syn: forecaster,
         predictor, prognosticator, soothsayer]
    2: information that supports a probabilistic estimate of future
       events; "the weekly bulletin contains several predictors of
       mutual fund performance"
    3: a computer for controlling antiaircraft fire that computes
       the position of an aircraft at the instant of a shell's
       arrival