The Collaborative International Dictionary of English v.0.48:

Pounce \Pounce\, n. [F. ponce pumice, pounce, fr. L. pumex,
   -icis, pumice. See Pumice.]
   1. A fine powder, as of sandarac, or cuttlefish bone, --
      formerly used to prevent ink from spreading on manuscript.
      [1913 Webster]

   2. Charcoal dust, or some other colored powder for making
      patterns through perforated designs, -- used by
      embroiderers, lace makers, etc.
      [1913 Webster]

   Pounce box, a box for sprinkling pounce.

   Pounce paper, a transparent paper for tracing.
      [1913 Webster]