Source : Webster's Revised Unabridged Dictionary (1913)

Fathomable \Fath"om*a*ble\, a.
   Capable of being fathomed.

Source : WordNet®

fathomable
     adj 1: of depth; capable of being sounded or measured [ant: {unfathomable}]
     2: (of meaning) capable of being penetrated or comprehended