(n.) A square or oblong opening in a deck or floor, affording passage from one deck or story to another; the entrance to a cellar.

French door apse arcade arcature arch arched roof back door barway bulkhead camber carriage entrance ceilinged roof cellar door cellarway concameration concha cove cupola dome door doorjamb doorpost doorway front door gate gatepost gateway geodesic dome hatch hatchway igloo keystone lintel ogive porch portal porte cochere postern propylaeum pylon scuttle side door skewback span stile storm door threshold tollgate trap trap door turnpike turnstile vault vaulting voussoir