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.
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.