The Collaborative International Dictionary of English v.0.48:

Diviner \Di*vin"er\, n.
   1. One who professes divination; one who pretends to predict
      events, or to reveal occult things, by supernatural means.
      [1913 Webster]

            The diviners have seen a lie, and have told false
            dreams; they comfort in vain.         --Zech. x. 2.
      [1913 Webster]

   2. A conjecture; a guesser; one who makes out occult things.
      --Locke.
      [1913 Webster]

WordNet (r) 3.0 (2006):

diviner
    n 1: someone who claims to discover hidden knowledge with the
         aid of supernatural powers

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "diviner":
   Cassandra, Comus, Druid, Faust, astrologer, augur, calamity howler,
   conjurer, crystal gazer, diabolist, divinator, divineress, dowser,
   forecaster, foreknower, foreseer, foreshower, foreteller,
   fortuneteller, geomancer, haruspex, miracle-worker, necromancer,
   palmist, predictor, prefigurer, presager, prognosticator,
   prophesier, prophet, prophet of doom, prophetess, psychic,
   pythoness, religious prophets, seer, seeress, soothsayer, sorcerer,
   thaumaturge, thaumaturgist, theurgist, vates, warlock, water witch,
   weather prophet, wizard