The Collaborative International Dictionary of English v.0.48:

Smoothing \Smooth"ing\, a. & n.
   fr. Smooth, v.
   [1913 Webster]

   Smoothing iron, an iron instrument with a polished face,
      for smoothing clothes; a sadiron; a flatiron.

   Smoothing plane, a short, finely set plane, for smoothing
      and finishing work.
      [1913 Webster]

WordNet (r) 3.0 (2006):

smoothing iron
    n 1: home appliance consisting of a flat metal base that is
         heated and used to smooth cloth [syn: iron, smoothing
         iron]