1. 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.
2. (Science: chemical) Any thick mass of rock which prevents miners from following the lode or vein.
Origin: Prov. E. Jaumb, jaum, f. Jambe a leg, jambe de force a principal rafter. See Gambol.