FLUKE, a name given to several kinds of fish, flat in shape, especially to the common flounder; also to a trematode worm, resembling a flounder in shape, which, as a parasite, infects the liver and neighbouring organs of certain animals, especially sheep, and causes liver-rot. The most common is Fasciola hepatica (see TREMATODES). The name is given to a species of kidney potato; to the holding plates, triangular in shape, at the end of the arms of an anchor; and to the triangular extremities of the tail of a whale. The use of the word as a slang expression for a lucky accident appears to have been first applied in billiards to an unintentional scoring shot.