is a window forming a bav or recess in a room, and projecting outwards from the wall either in a rectangular, polygonal, or semicircular form, often called a bow- window. Bay-windows do not appear to have been used earlier than the Perpendicular style; but at that period they were very frequently employed, particularly in halls, where they are invariably found at one end, and sometimes at both ends, of the dais; and the lights are generally considerably longer than those of the other windows, so as to reach much nearer to the floor. Semicircular bay-windows were not used till Gothic architecture had begun to lose its purity, and were at no period so common as the other forms. Windows of this kind are sometimes used in upper stories, and in such cases are supported on corbels or on projecting suites of mouldings. — SEE ORIEL.