(dated) A very cold night.

plural of three-dog night

(UK) Alternative form of all cats are grey in the dark

(US) Alternative form of all cats are grey in the dark

(informal, humorous) Frightening imagined creatures; ghosts or other supernatural beings.

Alternative form of all cats are grey in the dark

A medium-sized heron, Nycticorax nycticorax, found throughout a large part of the world, except in the coldest regions and Australasia.

Implies that somebody died.

plural of black-crowned night heron

(euphemistic) To die without protest.