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

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "predictor":
   Cassandra, Druid, astrologer, augur, calamity howler,
   crystal gazer, divinator, diviner, divineress, forecaster,
   foreknower, foreseer, foreshower, foreteller, fortuneteller,
   geomancer, haruspex, palmist, prefigurer, presager, prognosticator,
   prophesier, prophet, prophet of doom, prophetess, psychic,
   pythoness, religious prophets, seer, seeress, soothsayer, vates,
   weather prophet