fluke 2 
(flk)
(flk)n.
1. Nautical The triangular blade at the end of an arm of an anchor, designed to catch in the ground.
2. A barb or barbed head, as on an arrow or a harpoon.
3. Either of the two horizontally flattened divisions of the tail of a whale.
[Possibly from FLUKE1.]
fluke2top: arrowhead and whale flukes
bottom: anchor flukes