The Collaborative International Dictionary of English v.0.48:

Surmise \Sur*mise"\, v. t. [imp. & p. p. Surmised; p. pr. &
   vb. n. Surmising.]
   To imagine without certain knowledge; to infer on slight
   grounds; to suppose, conjecture, or suspect; to guess.
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         It wafted nearer yet, and then she knew
         That what before she but surmised, was true. --Dryden.
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         This change was not wrought by altering the form or
         position of the earth, as was surmised by a very
         learned man, but by dissolving it.       --Woodward.
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