Brit used to denote extreme cold
brass monkey weather
cold enough to freeze the balls of a brass monkey
often wrongly supposed to be connected with the former storage of cannonballs on warships in racks or ‘monkeys’, from which the balls supposedly fell out when they contracted in cold weather; more likely the image is a stock one of real monkeys, and an 1830s source refers to ‘a tone of voice which set me shaking like a monkey in frosty weather’