The presidents veto meant the knell of all the valiant efforts to tighten gun controls.
At noon we heard the bells that were the death knell in memory of the fire victims.
The advent of unions were the death knell for many employers.
As the mourners gathered at the graveside, they heard the solemn knell of the church bell.
When it has a subject, verb, punctuation, capitalization, a predicate, and a complete thought. A sentence is a sentence when it is handed down by a judge (or a magistrate).