1) British clothing 
The bowler hat, also known as a bob hat, derby (US), billycock or bombín, is a hard felt hat with a rounded crown originally created in 1849 for the British soldier and politician Edward Coke, the younger brother of the 2nd Earl of Leicester. The bowler hat was popular with the working class during the Victorian era, and later on with the middle ...
Bowler Hat is London Cockney rhyming slang for a rat.
[n] - a hat that is round and black and hard with a narrow brim
bowler noun a felt hat that is round and hard with a narrow brim