The term 'DOOMSDAY' is often used to refer to a catastrophic event that will bring about the END of the world. The crossword solutions for this term are END, which stands for the END of something, and DAY, which is a 24-hour period of time. Together, these two words form the phrase 'the END of the DAY, ' which is often used to refer to a time of great destruction or upheaval. DOOMSDAY, then, is the time when the world will come to an END.