Illustrated Companion to the Latin Dictionary/Tympanium

This article incorporates text from a publication now in the public domain: Rich, Anthony (1849). The illustrated companion to the Latin dictionary, and Greek lexicon. p. vi. OCLC 894670115. https://archive.org/details/illustratedcompa00rich. 

TYMPAN'IUM (τυμπάνιον). Diminutive of TYMPANUM; a pearl with one surface flat and the other round (Plin. H. N. ix. 44.), like a kettle-drum, from which resemblance it is believed that the name arose.