Source : Webster's Revised Unabridged Dictionary (1913)

Conjecture \Con*jec"ture\ (; 135?), n. [L. conjectura, fr.
   conjicere, conjectum, to throw together, infer, conjecture;
   con- + jacere to throw: cf. F. conjecturer. See {Jet} a
   shooting forth.]
   An opinion, or judgment, formed on defective or presumptive
   evidence; probable inference; surmise; guess; suspicion.

         He [Herodotus] would thus have corrected his first
         loose conjecture by a real study of nature. --Whewell.

         Conjectures, fancies, built on nothing firm. --Milton.

Conjecture \Con*jec"ture\, v. t. [imp. & p. p. {Conjectured}; p.
   pr. & vb. n. {Conjecturing}.] [Cf. F. conjecturer. Cf.
   {Conject}.]
   To arrive at by conjecture; to infer on slight evidence; to
   surmise; to guess; to form, at random, opinions concerning.

         Human reason can then, at the best, but conjecture what
         will be.                                 --South.

Conjecture \Con*jec"ture\, v. i.
   To make conjectures; to surmise; to guess; to infer; to form
   an opinion; to imagine.

Source : WordNet®

conjecture
     n 1: 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}]
     2: a message expressing an opinion based on incomplete evidence
        [syn: {guess}, {supposition}, {surmise}, {surmisal}, {speculation},
         {hypothesis}]
     3: reasoning that involves the formation of conclusions from
        incomplete evidence
     v : to believe especially on uncertain or tentative grounds;
         "Scientists supposed that large dinosaurs lived in
         swamps" [syn: {speculate}, {theorize}, {theorise}, {hypothesize},
          {hypothesise}, {hypothecate}, {suppose}]