An unhappy ending is a conclusion to a story or situation that is not favorable. It is often characterized by tragedy, despair, and sorrow. In crossword puzzles, the terms 'DEMISE' (6 letters) and 'DOOM' (4 letters) are often used to describe an unhappy ending. DEMISE is defined as the end of something, while DOOM is defined as an inevitable and unavoidable fate. Together, these two words can be used to describe an unhappy ending.