The Collaborative International Dictionary
Tympan sheet
Tympan \Tym"pan\, n. [F., fr. tympanum a kettledrum, a panel of a door. See Tympanum, and cf. Tymp.]
A drum. [Obs.]
(Arch.) A panel; a tympanum.
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(Print.) A frame covered with parchment or cloth, on which the blank sheets are put, in order to be laid on the form to be impressed.
Tympan sheet (Print.), a sheet of paper of the same size as that to be printed, pasted on the tympan, and serving as a guide in laying the sheets evenly for printing.
--W. Savage.