British slang for very cold weather, short for colder than a brass monkey's tit. {Hmmm. And here I thought it was Colder than a witch's tit and Colder than the balls on a brass monkey.} Example: How cold is it? It's brass monkey.
BRASS MONKEY
Meaning of BRASS MONKEY in English
Slang English vocab. Английский сленговый словарь. 2012