Definition of brass monkey in English:

brass monkey

noun

informal
  • Used in phrases to refer to extremely cold weather.

    ‘it's brass monkey weather tonight’
    • ‘It got cold on the gun decks and the indentations in the brass monkey would get smaller than the iron cannonballs they were holding.’
    • ‘Similarly, pack your thermals, because it's colder than a brass monkey's ice lolly.’
    • ‘The entire cab area can be hosed out after a good day bush bashing, while the creature comforts included air conditioning good enough to freeze the balls off a brass monkey.’
    • ‘Thus, it was quite literally, ‘Cold enough to freeze the balls off a brass monkey!’’
    • ‘Actually the weather today is much milder than yesterday when it was cold enough to freeze the spheres off a brass monkey (an old sea-faring expression).’

Origin

Mid 19th century: often said to be from a type of brass rack or monkey in which cannonballs were stored and which contracted in very cold weather, ejecting the balls, but this explanation has not been proved.

Pronunciation

brass monkey

/ˈˌbras ˈməNGkē/