Definition of Monmouth cock in US English:

Monmouth cock

noun

historical
  • A style of wearing a broad-brimmed hat turned up at the back and tipped over the eyes, fashionable for a few years from about 1667; a hat worn in this style.

Origin

Early 18th century; earliest use found in Joseph Addison (1672–1719), writer and politician. From the name of James Scott, Duke of Monmouth, illegitimate son of King Charles II and leader of the rebellion of 1685 + cock.