The Collaborative International Dictionary of English v.0.48:

Planer \Plan"er\, n.
   1. One who, or that which, planes; a planing machine; esp., a
      machine for planing wood or metals.
      [1913 Webster]

   2. (Print.) A wooden block used for forcing down the type in
      a form, and making the surface even. --Hansard.
      [1913 Webster]

   Planer centers. See under Center.
      [1913 Webster]

WordNet (r) 3.0 (2006):

planer
    n 1: a power tool for smoothing or shaping wood [syn: plane,
         planer, planing machine]