DEFINITION OF LEADING ARCHITECTURAL TERMS[482] _Abacus_--the flat member at the top of a capital. _Apse_--the semicircular space at the end of a building. _Arcade_--a series of arches; is usually applied to the small ornamental arches only. _Barrel vault_--resembling the inside of a barrel. _Bead_--a small round moulding. _Boss_--a projecting ornament in a vault at the intersection of the ribs. _Canopy_--the head of a niche over an image; also the ornamental moulding over a door or window or tomb. _Capital_, _cap_--the head of a column, pilaster, etc. _Chamfer_--a sloping surface forming the bevelled edge of a square pier, moulding, or buttress, when the angle is said to be chamfered off. _Chevron_--an inflected moulding, also called zigzag, characteristic of Norman architecture. _Clere-story_ or _clear-story_--the upper story of a church, as distinguished from the triforium or blind story below it, in which the openings, though resembling windows, are usually blank or blind, not glazed. _Corbel_--a projecting stone to carry a weight, usually carved. _Crocket_--an ornament usually resembling a leaf half opened, and projecting from the upper edge of a canopy or pyramidal covering. The term is supposed to be derived from the resemblance to a shepherd's crook. _Crypt_--a vault beneath a church, generally beneath the chancel only, and sometimes used for the exhibition of relics. _Cusp_--an ornament used in the tracery of windows, screens, etc., to form foliation. _Dormer_--an upright window placed on a sloping roof, giving light to the chambers next the roof. _Fillet_--a small square band used on the face of mouldings. _Finial_--the ornament which finishes the top of a pinnacle, a canopy, or a spire, usually carved into a bunch of foliage. _Flying buttress_--an arch carried over the roof of an aisle from the external buttress to the wall of the clerestory, to support the vault. _Gargoyle_--a projected water-spout, often ornamented with grotesque figures. _Jambs_--the sides of a window opening or doorway. _Mullion_--the vertical bar dividing the lights of a window. _Ogee_--a moulding formed by the combination of a round and hollow. _Pier arches_--the main arches of the nave or choir resting on piers. _Pinnacle_--a sort of small spire usually terminating a buttress. _Piscina_--a water-drain in a church placed on the right-hand side of an altar for the use of the priest. _Plinth_--the projecting member forming the lower part of a base or of a wall. _Shaft_--a small, slender pillar usually attached to a larger one, or in the sides of a doorway or window. _Slype_--a passage leading from the transept to the chapter-house. _String-course_--a horizontal moulding or course of masonry, usually applied to the one carried under the windows of the chancel, both externally and internally. _Tooth ornament_--an ornament resembling a row of teeth, sometimes called dog's tooth and shark's tooth. _Transept_--the portion of a building crossing the nave and