Demise means death or the end of something important. When a newspaper reports the demise of a famous person, it's announcing their death. When historians discuss the demise of the Roman Empire, they're talking about how that mighty civilization gradually fell apart and disappeared.

The word carries a sense of finality and significance. You wouldn't use demise to describe finishing your homework or losing a pencil. Instead, it fits situations where something meaningful comes to an end: the demise of a once-powerful company, the demise of an old tradition, or the demise of the dinosaurs 66 million years ago.

In legal contexts, demise can also mean transferring property or an estate after someone dies. A king's lands might pass to his heir upon his demise.

The word sounds formal and serious because it usually describes serious matters. While “death” and “end” work in everyday conversation, demise adds weight and gravity to what you're describing. If someone says “the demise of Saturday morning cartoons,” they're emphasizing how completely that era ended, not just that it slowly changed or faded away.