Tympan /(?)/

Tym·pan

Tympan

n.
  1. A drum. [Obs.]
  2. A panel; a tympanum. (Arch.)
  3. 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. (Print.)

Phrases & Compounds
Tympan sheet
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.