The Collaborative International Dictionary of English v.0.48:

Stencil \Sten"cil\, n. [Probably from OF. estincelle spangle,
   spark, F. ['e]tincelle spark, L. scintilla. See
   Scintillate, and cf. Tinsel.]
   A thin plate of metal, leather, or other material, used in
   painting, marking, etc. The pattern is cut out of the plate,
   which is then laid flat on the surface to be marked, and the
   color brushed over it. Called also stencil plate.
   [1913 Webster]