Brass monkey refers to a popular colloquial expression, “Brass monkey weather” used to describe extremely cold climatic conditions.
Today, the phrase is used synonymously to the word cold.
Although the exact origin of the phrase is not known, its roots may be traced back to the mid-19th century, when trade with East Asian countries, such as China and Japan started facilitating for English speaking vessels, due to the successes of the Opium Wars as well as the Perry Expedition.
The origin of the colloquialism is linked to the fact that “Brass monkey” statuettes were a popular souvenir and trading good, imported to the West from Asian countries.
“Brass monkey” was used as a reference to cold in many contexts by the 1840’s, and especially in the 1850’s, with accounts either likening the cold to the temperature of a brass monkey, or describing the temperature as so freezing, that it could freeze off various body part of a “Brass monkey” statue.
In the later decades of the 1800’s, the expression’s popularity grew significantly, well into the 20th century.
Following the 1950’s, it somewhat died down, however it was brought back to popularity in the 1980’s, thanks to the appearance of musical pieces, such as Beastie Boys’ song “Brass Monkey”, released on their album, “Licenced to Ill” in 1986.
“Brass monkey” gained some more popularity on the internet, first appearing on Urban Dictionary in 2003, with countless other entries appearing in the subsequent years.