[tym.pa.num] n, pl -na also -nums [ML & L; ML, eardrum, fr. L, drum, architectural panel, fr. Gk tympanon drum, kettledrum; perh. akin to Gk typtein to beat] (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 usu. 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