The Collaborative International Dictionary of English v.0.48:

Soothsay \Sooth"say`\, v. i. [Sooth + say; properly to say
   truth, tell the truth.]
   To foretell; to predict. "You can not soothsay." --Shak. "Old
   soothsaying Glaucus' spell." --Milton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Soothsay \Sooth"say`\, n.
   1. A true saying; a proverb; a prophecy. [Obs.] --Spenser.
      [1913 Webster]

   2. Omen; portent. Having
      [1913 Webster]

            God turn the same to good soothsay.   --Spenser.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "soothsay":
   adumbrate, augur, call, cast a horoscope, cast a nativity, divine,
   dope, dope out, dowse for water, forebode, forecast, foresee,
   foretell, fortune-tell, guess, hariolate, make a prediction,
   make a prognosis, make a prophecy, portend, predict, prefigure,
   presage, prognosticate, prophesy, read palms, read tea leaves,
   read the future, speculate, tell fortunes, tell the future,
   vaticinate