brass monkey

Etymology
From the phrase. According to the U.S. Naval Historical Center, which cites the Random House Historical Dictionary of American Slang, 'the first recorded use of the term "brass monkey" appears to dates [sic] to 1857 when it was used in an apparently vulgar context by C.A. Abbey in his book Before the Mast in the Clippers, where on page 108 it says "It would freeze the tail off a brass monkey."' A number of false etymologies have been suggested. For more information, see.

Adjective

 * 1)  Very cold.