The Collaborative International Dictionary of English v.0.48:

Speculation \Spec`u*la"tion\, n. [L. speculatio a spying out,
   observation: cf. F. sp['e]culation.]
   1. The act of speculating. Specifically:
      [1913 Webster]
      (a) Examination by the eye; view. [Obs.]
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      (b) Mental view of anything in its various aspects and
          relations; contemplation; intellectual examination.
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                Thenceforth to speculations high or deep
                I turned my thoughts.             --Milton.
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      (c) (Philos.) The act or process of reasoning a priori
          from premises given or assumed.
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      (d) (Com.) The act or practice of buying land, goods,
          shares, etc., in expectation of selling at a higher
          price, or of selling with the expectation of
          repurchasing at a lower price; a trading on
          anticipated fluctuations in price, as distinguished
          from trading in which the profit expected is the
          difference between the retail and wholesale prices, or
          the difference of price in different markets.
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                Sudden fortunes, indeed, are sometimes made in
                such places, by what is called the trade of
                speculation.                      --A. Smith.
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                Speculation, while confined within moderate
                limits, is the agent for equalizing supply and
                demand, and rendering the fluctuations of price
                less sudden and abrupt than they would otherwise
                be.                               --F. A.
                                                  Walker.
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      (e) Any business venture in involving unusual risks, with
          a chance for large profits.
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   2. A conclusion to which the mind comes by speculating; mere
      theory; view; notion; conjecture.
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            From him Socrates derived the principles of
            morality, and most part of his natural speculations.
                                                  --Sir W.
                                                  Temple.
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            To his speculations on these subjects he gave the
            lofty name of the "Oracles of Reason." --Macaulay.
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   3. Power of sight. [Obs.]
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            Thou hast no speculation in those eyes. --Shak.
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   4. A game at cards in which the players buy from one another
      trumps or whole hands, upon a chance of getting the
      highest trump dealt, which entitles the holder to the pool
      of stakes.
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WordNet (r) 3.0 (2006):

speculation
    n 1: a message expressing an opinion based on incomplete
         evidence [syn: guess, conjecture, supposition,
         surmise, surmisal, speculation, hypothesis]
    2: a hypothesis that has been formed by speculating or
       conjecturing (usually with little hard evidence);
       "speculations about the outcome of the election"; "he
       dismissed it as mere conjecture" [syn: speculation,
       conjecture]
    3: an investment that is very risky but could yield great
       profits; "he knew the stock was a speculation when he bought
       it" [syn: speculation, venture]
    4: continuous and profound contemplation or musing on a subject
       or series of subjects of a deep or abstruse nature; "the
       habit of meditation is the basis for all real knowledge"
       [syn: meditation, speculation]

Moby Thesaurus II by Grady Ward, 1.0:

126 Moby Thesaurus words for "speculation":
   abstraction, actuarial prediction, advisement, agiotage, analysis,
   apocalypse, arbitrage, betting, blind guess, bold conjecture,
   brainwork, brooding, buying in, calculated risk, cardsharping,
   casting lots, cerebration, chance, cogitation, conjecture,
   consideration, contemplation, counsel, deliberation, doctrinairism,
   doctrinality, doctrinarity, equity capital, evaluation,
   excogitation, explanation, flier, flutter, foreboding, forecast,
   forecasting, foreshowing, foresight, foretelling, fortune, gamble,
   gambling, gaming, guess, guesswork, hazard, hazarding, hunch,
   hypothesis, improbability, investment, liquidation, luck,
   lucubration, meditation, mere theory, musing, omen, opinion,
   perhaps, play, playing, plunge, pondering, postulation, prediction,
   prefiguration, prefigurement, prefiguring, presage, presaging,
   presentiment, preshowing, presignifying, prime investment,
   probability, profit taking, prognosis, prognostication, promise,
   prophecy, prophesying, prospectus, reflection, review, revolving,
   risk, risking, rough guess, round trade, rumination, scalping,
   shot, soothsay, sortition, sporting, spot sale, stab, staking,
   statistical prediction, stockjobbery, stockjobbing, study,
   studying, suppose, supposition, surmise, theoretic,
   theoretical basis, theoretics, theoria, theoric, theorization,
   theory, thinking, turn, uncertainty, unverified supposition,
   vaticination, venture, venture capital, wager, wagering, weighing,
   wild guess, wondering



Bouvier's Law Dictionary, Revised 6th Ed (1856):

SPECULATION, contracts. The hope or desire of making a profit by the
purchase and resale of a thing. Pard. Dr. Com. n. 12. The profit so made;
as, be made a good speculation.