Real Dictionary

derby
The Derby is the name of a race for three-year-old horses that takes place each year. In Britain, it refers to a race that takes place in Epsom. In the United States, it refers particularly to the Kentucky Derby.
countable noun: A derby is a sporting event involving teams from the same area or city.

Derby in American English 1
a race for three-year-old horses, run annually at Epsom Downs in Surrey
noun: a race for three-year-old horses that is run annually at Epsom Downs, near London, England: first run in 1780

Derby in American English 2
city in Derbyshire, central England: county district pop. 219,000
noun: a city in Derbyshire, in central England. 215,200

derby in British English
noun: a stiff felt hat with a rounded crown and narrow curved brim

Derby in British English 1
noun

Derby in British English 2
noun: a city in central England, in Derby unitary authority, Derbyshire: engineering industries (esp aircraft engines and railway rolling stock); university (1991). Pop: 229 407 (2001)

Derby in British English 3
noun: Earl of. title of Edward George Geoffrey Smith Stanley. 1799–1869, British statesman; Conservative prime minister (1852; 1858–59; 1866–68)