FID

noun

1. 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. A square bar of wood or iron, with a shoulder at one end, to support the weight of the topmast (on a ship).
3. A plug of oakum for the vent of a gun.

verb

1. To support a topmast using a fid.