fath·om (fāth'əm) n.
Abbr. fth. or fm. A unit of length equal to 6 feet (1.83 meters), used principally in the measurement and specification of marine depths. tr.v.
fath·omed, fath·om·ing, fath·oms
To penetrate to the meaning or nature of; comprehend.
To determine the depth of; sound.
[Middle English fathme, from Old English fæthm, outstretched arms; see petə- in Indo-European roots.] fath'om·a·ble adj.
(fāth'əm) 
