fathom

/ˈfæðəm/
verb
  1. To understand or comprehend something deeply.
    • I cannot fathom why she would quit her job without another one lined up.
    • It's hard to fathom the scale of the universe.
    • He tried to fathom the meaning of the ancient poem.
noun
  1. A unit of length equal to six feet, used mainly for measuring the depth of water.
    • The map showed a depth of 15 fathoms near the reef.
    • The sailor dropped the line and found the water was 10 fathoms deep.
    • The submarine descended to a depth of 200 fathoms.