What is the X in X-mas?
"drum of the ear," 1610s, from Medieval Latin tympanum, introduced in this sense by Italian anatomist Gabriello Fallopio (1523-1562), from Latin tympanum "drum," from Greek tympanon "a drum, panel of a door," from root of typtein "to beat, strike" (see type (n.)). Cf. Old English timpan "drum, timbrel, tambourine," from Latin tympanum. The modern meaning "a drum" is attested in English from 1670s.