brass monkey
noun
- informal used in phrases to refer to extremely cold weather〈非正式〉猴儿冷（用于短语中, 指天气特别冷）：
it's brass monkey weather tonight
今晚特别冷
it was cold enough to freeze the balls off a brass monkey.
天太冷, 快要把下巴都冻掉了。
词源
late 19th cent.: from a type of brass rack or 'monkey' in which cannonballs were stored and which contracted in very cold weather， ejecting the balls.