The Whippet (also English Whippet or Snap Dog) is a dog breed of medium size. They are a sighthound breed that originated in England, where they descended from Greyhounds. Whippets today still strongly resemble a smaller Greyhound. Part of the Hound group, Whippets have relatively few health problems other than arrhythmia. Whippets also participate in dog sports such as lure coursing, agility, dock diving and flyball. The name is derived from an early-17th-century word, now obsolete, meaning "to move briskly".There has been continuity in describing Greyhound-types of different sizes: large, medium and small, as recorded in hunting manuals and works on natural history from the Middle Ages. Edward of Norwich, 2nd Duke of York confirmed in his early-15th-century translation and additions to the original late 14th century French Livre de chasse the advantage of maintaining the great, the middle, and the small size of greyhound for different sorts of game. The English physician and academic John Caius refers in his 16th century De Canibus Britannicus to lesser as well as greater sorts of Leporarius, Grehounde (greyhound) and notably to a type which has been connected to the Whippet, the Tumbler, a lesser sort of mungrell Greyhounde and excellent warren dog for catching rabbits, also recorded by the early-19th-century Scottish curator and editor Thomas Brown. The Victorian English writers describe the emerging modern breed of Whippet or snap-dog bred for catching rabbits, coursing competitions, straight rag-racing, and for the novel show fancy.This has led to Whippets being described as "the poor man's greyhound " They are a popular companion breed frequently used in amateur racing, lure coursing, and dog shows; they have the highest running speed of breeds for their weight: and are possibly the fastest accelerating dog breed.