Source : Webster's Revised Unabridged Dictionary (1913)

Jamb \Jamb\, n. [Prov. E. jaumb, jaum, F. jambe a leg, jambe de
   force a principal rafter. See {Gambol}.]
   1. (Arch) The vertical side of any opening, as a door or
      fireplace; hence, less properly, any narrow vertical
      surface of wall, as the of a chimney-breast or of a pier,
      as distinguished from its face. --Gwilt.

   2. (Mining) Any thick mass of rock which prevents miners from
      following the lode or vein.

Jamb \Jamb\, v. t.
   See {Jam}, v. t.

Source : WordNet®

jamb
     n : upright consisting of a vertical side member of a door or
         window frame