Merriam-Webster Collegiate Dictionary - tympanum

 noun  (plural tympana; also -nums)  Etymology: Medieval Latin & Latin; Medieval Latin, eardrum, from Latin, drum, architectural panel, from Greek tympanon drum, kettledrum; perhaps akin to Greek typtein to beat  Date: 1619  1.  a.  (1) tympanic membrane  (2) middle ear  b. a thin tense membrane covering an organ of hearing of an insect — see insect illustration  c. a membranous resonator in a sound-producing organ  2.  a. the recessed usually triangular face of a pediment within the frame made by the upper and lower cornices  b. the space within an arch and above a lintel or a subordinate arch