The Collaborative International Dictionary of English v.0.48:

Suppose \Sup*pose"\, v. t. [imp. & p. p. Supposed; p. pr. &
   vb. n. Supposing.] [F. supposer; pref. sub- under + poser
   to place; -- corresponding in meaning to L. supponere,
   suppositum, to put under, to substitute, falsify,
   counterfeit. See Pose.]
   1. To represent to one's self, or state to another, not as
      true or real, but as if so, and with a view to some
      consequence or application which the reality would involve
      or admit of; to imagine or admit to exist, for the sake of
      argument or illustration; to assume to be true; as, let us
      suppose the earth to be the center of the system, what
      would be the result?
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            Suppose they take offence without a cause. --Shak.
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            When we have as great assurance that a thing is, as
            we could possibly, supposing it were, we ought not
            to make any doubt of its existence.   --Tillotson.
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   2. To imagine; to believe; to receive as true.
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            How easy is a bush supposed a bear!   --Shak.
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            Let not my lord suppose that they have slain all the
            young men, the king's sons; for Amnon only is dead.
                                                  --2 Sam. xiii.
                                                  32.
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   3. To require to exist or to be true; to imply by the laws of
      thought or of nature; as, purpose supposes foresight.
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            One falsehood always supposes another, and renders
            all you can say suspected.            --Female
                                                  Quixote.
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   4. To put by fraud in the place of another. [Obs.]
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   Syn: To imagine; believe; conclude; judge; consider; view;
        regard; conjecture; assume.
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The Collaborative International Dictionary of English v.0.48:

Suppose \Sup*pose"\, v. i.
   To make supposition; to think; to be of opinion. --Acts ii.
   15.
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The Collaborative International Dictionary of English v.0.48:

Suppose \Sup*pose"\, n.
   Supposition. [Obs.] --Shak. "A base suppose that he is
   honest." --Dryden.
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WordNet (r) 3.0 (2006):

suppose
    v 1: express a supposition; "Let us say that he did not tell the
         truth"; "Let's say you had a lot of money--what would you
         do?" [syn: suppose, say]
    2: expect, believe, or suppose; "I imagine she earned a lot of
       money with her new novel"; "I thought to find her in a bad
       state"; "he didn't think to find her in the kitchen"; "I
       guess she is angry at me for standing her up" [syn: think,
       opine, suppose, imagine, reckon, guess]
    3: to believe especially on uncertain or tentative grounds;
       "Scientists supposed that large dinosaurs lived in swamps"
       [syn: speculate, theorize, theorise, conjecture,
       hypothesize, hypothesise, hypothecate, suppose]
    4: take for granted or as a given; suppose beforehand; "I
       presuppose that you have done your work" [syn: presuppose,
       suppose]
    5: require as a necessary antecedent or precondition; "This step
       presupposes two prior ones" [syn: presuppose, suppose]

Moby Thesaurus II by Grady Ward, 1.0:

113 Moby Thesaurus words for "suppose":
   account, account as, adjudge, adjudicate, allegorize, allow,
   allude to, assume, be afraid, be judicious, believe, bring to mind,
   coin, conceit, conceive, conceptualize, conclude, concoct,
   conjecture, connote, consider, count, create, daresay, deduce,
   deem, divine, dream, dream up, entail, esteem, estimate,
   exercise judgment, expect, experience imaginatively,
   express an opinion, fabricate, fancy, fantasize, feel,
   fictionalize, form an opinion, gather, grant, guess, hatch,
   have a hunch, have an idea, have an impression, have an inkling,
   have the idea, hint, hold, hold as, hypothesize, ideate, imagine,
   implicate, imply, import, infer, insinuate, intimate, invent,
   involve, judge, let, let be, look upon as, maintain, mean,
   mean to say, mold, opine, originate, perhaps, pine,
   point indirectly to, posit, postulate, prefigure, presume,
   presuppose, presurmise, pretend, produce, provisionally accept,
   reckon, regard, repute, say, set down as, shape, speculation,
   suggest, supposition, surmise, suspect, take, take for,
   take for granted, take it, take to be, theorize, think,
   think likely, think of, think up, trow, understand, venture to say,
   view as, ween