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.
