in Naval Architecture, is a piece of curved timber fixed behind the lower part of the stern, immediately above the foremast end of the keel.

APRON is also a name given to a platform or flooring of plank, raised at the entrance of a dock, against which the dock gates are shut.

in Gunnery, a piece of lead which caps or covers the vent or touch-hole of a great gun.

APSIDA or Apsis, signifies the bowed or arched roof of a house, room, or oven, &c. as also the ring or compass of a wheel.