Derby an annual flat horse race for three-year-olds, founded in 1780 by the 12th Earl of Derby. The race is run on Epsom Downs in England on Derby Day in late May or early June. The name is also used for a similar race elsewhere, as in the Irish Derby.

In North American usage, a derby is a bowler hat, said to be from American demand for a hat of the type worn at the Epsom Derby.
Derby Dog a dog appearing on the racecourse after this has been cleared; taken proverbially as something sure to turn up or come in the way. The term is recorded from the mid 19th century.

Derby City and county district on the River Derwent, Derbyshire, central England. Known for its Derby ware china, manufactured here since c.1750. Industries: railway and aerospace engineering, textiles, ceramics. Pop. (1996 est.) 234,000.

Der·by ¹ / ˈdärbē/ a city in north central England, on the Derwent River ; pop. 214,000.