\Fid\, n. [Prov. E. fid a small, thick lump.]
1. (Naut.) A square bar of wood or iron, used to support the
   topmast, being passed through a hole or mortise at its
   heel, and resting on the trestle trees.
2. A wooden or metal bar or pin, used to support or steady
   anything.
3. A pin of hard wood, tapering to a point, used to open the
   strands of a rope in splicing.
Note: There are hand fids and standing fids (which are larger
      than the others, and stand upon a flat base). An iron
      implement for this purpose is called a marline spike.
4. (Mil.) A block of wood used in mounting and dismounting
   heavy guns.