The Collaborative International Dictionary of English v.0.48:

Gib \Gib\, n. [Etymol. uncertain.]
   A piece or slip of metal or wood, notched or otherwise, in a
   machine or structure, to hold other parts in place or bind
   them together, or to afford a bearing surface; -- usually
   held or adjusted by means of a wedge, key, or screw.
   [1913 Webster]

   Gib and key, or Gib and cotter (Steam Engine), the fixed
      wedge or gib, and the driving wedge,key, or cotter, used
      for tightening the strap which holds the brasses at the
      end of a connecting rod.
      [1913 Webster]