The Collaborative International Dictionary of English v.0.48:
Fathom \Fath"om\, v. t. [imp. & p. p. Fathomed; p. pr. & vb.
1. To encompass with the arms extended or encircling; to
measure by throwing the arms about; to span. [Obs.]
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.
The page of life that was spread out before me
seemed dull and commonplace, only because I had not
fathomed its deeper import. --Hawthotne.