The Collaborative International Dictionary
Fluke \Fluke\ (fl[=u]k or fl[=oo]k), n. [Cf. AS. fl[=o]c a kind of flatfish, Icel. fl[=o]ki a kind of halibut.]
(Zo["o]l.) The European flounder. See Flounder. [Written also fleuk, flook, and flowk.]
(Zo["o]l.) Any American flounder of the genus Paralichthys, especially Paralicthys dentatus, found in the Atlantic Ocean and in adjacent bays.
--RHUD(Zo["o]l.) A parasitic trematode worm of several species, having a flat, lanceolate body and two suckers. Two species ( Fasciola hepatica and Distoma lanceolatum) are found in the livers of sheep, and produce the disease called rot.
Wikipedia
Fasciola hepatica, also known as the ' common liver fluke' or sheep liver fluke, is a parasitic trematode (fluke or flatworm, a type of helminth) of the class Trematoda, phylum Platyhelminthes. It infects the livers of various mammals, including humans. The disease caused by the fluke is called fasciolosis or fascioliasis, which is a type of helminthiasis and has been classified as a neglected tropical disease. Fasciolosis is currently classified as a plant/food-borne trematode infection, often acquired through eating the parasite metacercariae encysted on plants. F. hepatica which is distributed worldwide has been known as an important parasite of sheep and cattle for many years and causes great economic losses to these livestock species, up to £23 million in the UK alone. Because of its size and economic importance, it has been the subject of many scientific investigations and may be the best-known of any trematode species. F. hepatica's closest relative is Fasciola gigantica. These two flukes are sister species; they share many morphological features and can mate with each other.