fid

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Nautical A square bar used as a support for a topmast.
2. n. A large tapering pin used to open the strands of a rope before splicing.

Century Dictionary and Cyclopedia

1. n. A small thick lump.
2. n. A piece or plug of tobacco.
3. n. A bar of wood or metal used to support or steady anything.
4. n. Nautical: A square bar of wood or iron, with a shoulder at one end, used to support a topmast or topgallantmast when swayed up into place. The fid passes through a square hole in the heel of its mast, and its ends rest on the trestletrees.
5. n. A conical pin of hard wood, from 12 to 24 inches long, and from 1 to 3 inches in diameter at the butt, used to open the strands of rope in splicing.
6. Nautical, to sway into place and secure (a topmast or topgallantmast) by its fid. Also fidd.

Wiktionary

1. n. nautical A pointed tool without any sharp edges, used in weaving or knotwork to tighten and form up weaves or complex knots; used in sailing ships to open the strands of a rope before splicing. Compare marlinespike.
2. n. nautical A square bar of wood or iron, with a shoulder at one end, to support the weight of the topmast (on a ship).
3. n. A plug of oakum for the vent of a gun.
4. n. A small thick piece of anything.
5. n. A wooden or metal bar or pin, used to support or steady anything.
6. n. A naval euphemism for "penis", derived from the similarity of each of the above to the male reproductive organ.
7. v. To support a topmast using a fid.

GNU Webster's 1913

1. n. (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. n. A wooden or metal bar or pin, used to support or steady anything.
3. n. A pin of hard wood, tapering to a point, used to open the strands of a rope in splicing.
4. n. (Mil.) A block of wood used in mounting and dismounting heavy guns.