The Collaborative International Dictionary of English v.0.48:

Plancher \Planch"er\, n. [F., planche. See Planch.]
   1. A floor of wood; also, a plank. [Obs.] --Bacon.
      [1913 Webster]

   2. (Arch.) The under side of a cornice; a soffit.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Plancher \Planch"er\, v. t.
   To form of planks. [Obs.] --Golding.
   [1913 Webster]