The Collaborative International Dictionary of English v.0.48:

Open \O"pen\, n.
   Open or unobstructed space; clear land, without trees or
   obstructions; open ocean; open water. "To sail into the
   open." --Jowett (Thucyd.).
   [1913 Webster]

         Then we got into the open.               --W. Black.
   [1913 Webster]

   In open, In th open, in full view; without concealment;
      openly. [Obs.] --Beau. & Fl.
      [1913 Webster +PJC]