Source : Webster's Revised Unabridged Dictionary (1913)

Spanker \Spank"er\, n.
   1. One who spanks, or anything used as an instrument for
      spanking.

   2. (Naut.) The after sail of a ship or bark, being a
      fore-and-aft sail attached to a boom and gaff; --
      sometimes called {driver}. See Illust. under {Sail}.
      --Totten.

   3. One who takes long, quick strides in walking; also, a fast
      horse. [Colloq.]

   4. Something very large, or larger than common; a whopper, as
      a stout or tall person. [Colloq.]

   {Spanker boom} (Naut.), a boom to which a spanker sail is
      attached. See Illust. of {Ship}.