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Letter "O" Glossary

oculus (pl. oculi) — Round or oval openings, such as windows in a wall or openings in the crown or drum of a dome. In Gothic clerestory window design, an oculus with bar or plate tracery is usually located above the lancet windows.

ogee arch (ogive arch) — A delicate form of an arch with a pointed apex, formed by the intersection of two S curves used for decorative rather than structural purposes. Ogee arches were used only in the late Gothic period.

opus sectile — Images or patterns composed of individually shaped pieces of durable material, usually stone or glass, which form the design or pattern. Distinguished from "mosaics" which are compositions composed of numerous small pieces of glass or stone.

orant — A standing figure with arms raised, the conventional gesture of prayer in the Early Christian period.

order (architectural) — A specific ensemble of column (including base and capital) with an entablature characterized by distinctive forms and details. In Classical architecture, the three principal orders are Doric, Ionic and Corinthian.

oriel — A projection from the upper story of a building. Oriels may often contain windows.

orientation — The geographical position of a building according to the points of the compass. Most Christian churches are oriented on an east-west axis.

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