Tympanum

Tym′pa·num (tĭm′pȧ·nŭm), n.; pl. E. Tympanums (#), L. Tympana (#). [L., a kettledrum, a drum or wheel in machines, the triangular area in a pediment, the panel of a door, Gr. τύμπανον, τύπανον, fr. τύπτειν to strike, beat. See Type, and cf. Timbrel.] 1. (Anat.) (a) The ear drum, or middle ear. Sometimes applied incorrectly to the tympanic membrane. See Ear. (b) A chamber in the anterior part of the syrinx of birds.

2. (Zoöl.) One of the naked, inflatable air sacs on the neck of the prairie chicken and other species of grouse.

3. (Arch.) (a) The recessed face of a pediment within the frame made by the upper and lower cornices, being usually a triangular space or table. (b) The space within an arch, and above a lintel or a subordinate arch, spanning the opening below the arch.

4. (Mech.) 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.