OUTRIGGER is a 9 letter word that starts with O.

1. \Out"rig`ger\, n. (A["e]ronautics)
   A projecting frame used to support the elevator or tail
   planes, etc.
   
   

2. \Out"rig`ger\, n.
   1. Any spar or projecting timber run out for temporary use,
      as from a ship's mast, to hold a rope or a sail extended,
      or from a building, to support hoisting teckle.
   
   2. (Naut.)
      (a) A projecting support for a rowlock, extended from the
          side of a boat.
      (b) A boat thus equipped.
      (c) A projecting contrivance at the side of a boat to
          prevent upsetting, as projecting spars with a log at
          the end.