brass monkey used in various phrases to refer to extremely cold weather.

☞ Brass monkey comes from the mid-20th-century vulgar slang expression 'cold enough to freeze the balls off a brass monkey', the origin of which has been debated. One suggestion relates it to brass trays known as monkeys on which cannon balls were once stowed aboard warships.

1994Camping Magazine David will be doing his best to show you how to keep warm under canvas even if the temperature outside has dipped to brass monkey level.