Fluke is

• a name for some flounders, flat fishes. Many of the other meanings of the term derive from this flat shape.
• another name for trematoda, a class of flatworms, for example:
  • the liver fluke.
• either lobe of the tail of whales (cetaceans).
• a part of an anchor.
• a stroke of good luck; a chance event unlikely to occur again
• a manufacturer of electrical and electronic test equipment such as multimeters and oscilloscopes; see Fluke Corporation.
• a 1995 film; see Fluke (movie).
• the name of an electronic dance music band; see Fluke (band).
• also used against a person who has done something they would never be able to attempt again.