eardrum

n. membrane of the inner ear

The tympanic membrane, colloquially known as the eardrum, is a thin membrane that separates the external ear from the middle ear. Its function is to transmit sound vibrations from the air, conducted through the external acoustic meatus to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles.
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Ear·drum n. The thin, semitransparent, oval-shaped membrane that separates the middle ear from the external ear. [more]Eardrum - Community and Resources

Noun
1. the membrane in the ear that vibrates to sound
(synonym) tympanum, tympanic membrane, myringa
(hypernym) membrane, tissue layer
(hyponym) perforated eardrum
(part-holonym) ear
(part-meronym) umbo

(n.)
The tympanum. See Illust. of Ear.