a killing 'frost' [=weather that is so cold that the frost kills plants]
These plants should bloom until the first 'frost' of the season.
I have to 'frost' the birthday cake.
(..) He's hired thousands of foreign sellswords to bolster his army. But this storm is a stroke of luck for us northerners. Our people are used to fighting in the frost. His army is out there now suffering in the snow. One day I'll be Lord of Winterfell and Warden of the North. (..)2015 TvShow: Game of Thrones Title: The Gift Season: 5 Episode 7