1. The sound of a bell, especially when rung slowly for a death or funeral. This is the most common usage.
* Example: "The knell of the church bell tolled the hour of his passing."
2. A sign or indication of the end of something, often something important. This is a more figurative use.
* Example: "The closure of the factory was the knell for the town's economy."
In both meanings, "knell" signifies a finality, an ending, or a solemn announcement.