tympanum

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. ty`mpanon, ty`panon, fr. &unr_; 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. [ 1913 Webster ]

2. (Zool.) One of the naked, inflatable air sacs on the neck of the prairie chicken and other species of grouse. [ 1913 Webster ]

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. [ 1913 Webster ]

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. [ 1913 Webster ]