What is another word for three-dog night?
Pronunciation: [θɹˈiːdˈɒɡ nˈa͡ɪt] (IPA) 
Three-dog night is an old colloquial term that refers to a chilly night so cold, that to keep warm, one would need to cuddle up with three dogs. Some synonyms for the expression "three-dog night" are bone-chilling, freezing, icy, and bitter-cold. These terms are suitable for harsh weather conditions when the temperature drops below freezing point. Other synonyms include frosty, arctic, and glacial. As the expression suggests, the night is so freezing that three dogs would be needed to provide enough warmth to fight off the cold. Whatever the term used, it confirms the idea that the temperature outside is beyond cold and probably unbearable.
