[1] : The Collaborative International Dictionary of English v.0.48

guess \guess\ ge^s, v. t. imp.  p. p. guessed; p. pr. 
   vb. n. guessing. oe. gessen; akin to dan. gisse, sw.
   gissa, icel. gizha, d. gissen: cf. dan. giette to guess,
   icel. geta to get, to guess. probably originally, to try to
   get, and akin to e. get. see get.
   1. to form an opinion concerning, without knowledge or means
      of knowledge; to judge of at random; to conjecture.
      1913 webster

            first, if thou canst, the harder reason guess.
                                                  --pope.
      1913 webster

   2. to judge or form an opinion of, from reasons that seem
      preponderating, but are not decisive.
      1913 webster

            we may then guess how far it was from his design.
                                                  --milton.
      1913 webster

            of ambushed men, whom, by their arms and dress,
            to be taxallan enemies i guess.       --dryden.
      1913 webster

   3. to solve by a correct conjecture; to conjecture rightly;
      as, he who guesses the riddle shall have the ring; he has
      guessed my designs.
      1913 webster

   4. to hit upon or reproduce by memory. obs.
      1913 webster

            tell me their words, as near as thou canst guess
            them.                                 --shak.
      1913 webster

   5. to think; to suppose; to believe; to imagine; -- followed
      by an objective clause.
      1913 webster

            not all together; better far, i guess,
            that we do make our entrance several ways. --shak.
      1913 webster

            but in known images of life i guess
            the labor greater.                    --pope.

   syn: to conjecture; suppose; surmise; suspect; divine; think;
        imagine; fancy.

   usage: to guess, think, reckon. guess denotes, to
          attempt to hit upon at random; as, to guess at a thing
          when blindfolded; to conjecture or form an opinion on
          hidden or very slight grounds: as, to guess a riddle;
          to guess out the meaning of an obscure passage. the
          use of the word guess for think or believe, although
          abundantly sanctioned by good english authors, is now
          regarded as antiquated and objectionable by
          discriminating writers. it may properly be branded as
          a colloguialism and vulgarism when used respecting a
          purpose or a thing about which there is no
          uncertainty; as, i guess i 'll go to bed.
          1913 webster
see also:
guessed guessing get to guess think reckon 

[2] : The Collaborative International Dictionary of English v.0.48

guess \guess\, v. i.
   to make a guess or random judgment; to conjecture; -- with
   at, about, etc.
   1913 webster

         this is the place, as well as i may guess. --milton.
   1913 webster

[3] : The Collaborative International Dictionary of English v.0.48

guess \guess\, n.
   an opinion as to anything, formed without sufficient or
   decisive evidence or grounds; an attempt to hit upon the
   truth by a random judgment; a conjecture; a surmise.
   1913 webster

         a poet must confess
         his art 's like physic -- but a happy guess. --dryden.
   1913 webster

[4] : WordNet (r) 2.0

guess
     n 1: a message expressing an opinion based on incomplete evidence
          syn: conjecture, supposition, surmise, surmisal,
           speculation, hypothesis
     2: an estimate based on little or no information syn: guesswork,
         guessing, shot, dead reckoning
     v 1: 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
     2: put forward, of a guess, in spite of possible refutation; "i
        am guessing that the price of real estate will rise
        again"; "i cannot pretend to say that you are wrong" syn:
         venture, pretend, hazard
     3: judge tentatively or form an estimate of quantities or
        time; "i estimate this chicken to weigh three pounds"
        syn: estimate, gauge, approximate, judge
     4: guess correctly; solve by guessing; "he guessed the right
        number of beans in the jar and won the prize" syn: infer
see also:
conjecture supposition surmise surmisal speculation hypothesis 
guesswork guessing shot dead reckoning think 
opine suppose imagine reckon venture 
pretend hazard estimate gauge approximate 
judge infer 

[5] : Moby Thesaurus II by Grady Ward, 1.0

173 moby thesaurus words for "guess":
   account as, answer, appraise, appreciate, assess, assume,
   assumption, be afraid, believe, blind bargain, blind guess,
   bold conjecture, borderline case, bottom, call, cast a horoscope,
   cast a nativity, chance, class, clear up, conceive, conclude,
   conjecture, consider, contingency, crack, daresay, debug, decipher,
   decode, deduce, deem, disentangle, divine, do, dope, dope out,
   double contingency, dowse for water, esteem, estimate, evaluate,
   expect, explain, fancy, fathom, feel, feeling, figure, figure out,
   find out, find the answer, find the solution, forebode, forecast,
   foresee, foretell, form an estimate, fortune-tell, gamble, gauge,
   get, get right, give a guess, give an appreciation, guess right,
   guesstimate, guesswork, hariolate, have a hunch, have an idea,
   have an impression, have an inkling, have it, have the idea,
   hazard a conjecture, hit it, hold, hold as, hunch, hypothesis,
   hypothesize, imagine, interpret, judge, judgement, look upon as,
   maintain, make a prediction, make a prognosis, make a prophecy,
   make an estimation, make out, mark, measure, open question,
   open the lock, opine, perhaps, piece of guesswork, plumb,
   postulate, predict, prefigure, presage, presume, pretend, prize,
   prognosticate, prophesy, psych, psych out, puzzle out, question,
   rank, rate, ravel, ravel out, read palms, read tea leaves,
   read the future, reason, reckon, regard, resolve, riddle,
   risk assuming, rough guess, set down as, shot,
   sight-unseen transaction, solve, soothsay, sort out, speculate,
   speculation, stab, suppose, supposition, surmise, suspect,
   suspicion, take, take for, take it, tell fortunes, tell the future,
   tentatively suggest, theory, think, toss-up, touch and go, trow,
   undecided issue, undo, unlock, unravel, unriddle, unscramble,
   untangle, untwist, unverified supposition, unweave, valuate, value,
   vaticinate, venture a guess, view as, wager, ween, wild guess,
   work, work out

Guess >> G Words
Guess, definition of term: Guess
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