1911 Encyclopædia Britannica/Jamb

JAMB (from Fr. jambe, leg), in architecture, the side-post or lining of a doorway or other aperture. The jambs of a window outside the frame are called “reveals.” Small shafts to doors and windows with caps and bases are known as “jamb-shafts”; when in the inside arris of the jamb of a window they are sometimes called “scoinsons.”