The Collaborative International Dictionary of English v.0.48:

Fathom \Fath"om\, v. t. [imp. & p. p. Fathomed; p. pr. & vb.
   n. Fathoming.]
   1. To encompass with the arms extended or encircling; to
      measure by throwing the arms about; to span. [Obs.]
      --Purchas.
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   2. To measure by a sounding line; especially, to sound the
      depth of; to penetrate, measure, and comprehend; to get to
      the bottom of. --Dryden.
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            The page of life that was spread out before me
            seemed dull and commonplace, only because I had not
            fathomed its deeper import.           --Hawthotne.
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