Brown Driver Briggs

 1. to gather, restrain, fence, fortify, make inaccessible, enclose
  1) (Qal)
1a1. to cut off
1a2. fortified, cut off, made inaccessible (pass participle)
1a3. secrets, mysteries, inaccessible things (subst)
  2) (Niphal) to be withheld
  3) (Piel) to fortify