1. 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.
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. A block of wood used in mounting and dismounting heavy guns.
Origin: Prov. E. Fid a small, thick lump.