Source : Webster's Revised Unabridged Dictionary (1913)

Placket \Plack"et\, n. [F. plaquer to lay or clap on. See
   {Placard}.]
   1. A petticoat, esp. an under petticoat; hence, a cant term
      for a woman. [Obs.] --Beau. & Fl.

   2. The opening or slit left in a petticoat or skirt for
      convenience in putting it on; -- called also {placket
      hole}.

   3. A woman's pocket.