from
The Collaborative International Dictionary of English v.0.48
Fid \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.
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2. A wooden or metal bar or pin, used to support or steady
anything.
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3. A pin of hard wood, tapering to a point, used to open the
strands of a rope in splicing.
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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.
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4. (Mil.) A block of wood used in mounting and dismounting
heavy guns.
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