the ear drum, or middle ear. sometimes applied incorrectly to the tympanic membrane. see ear.-a chamber in the anterior part of the syrinx of birds.-one of the naked, inflatable air sacs on the neck of the prairie chicken and other species of grouse.-the recessed face of a pediment within the frame made by the upper and lower cornices, being usually a triangular space or table.-the space within an arch, and above a lintel or a subordinate arch, spanning the opening below the arch.-a drum-shaped wheel with spirally curved partitions by which water is raised to the axis when the wheel revolves with the lower part of the circumference submerged, -- used for raising water, as for irrigation.