You know when you cross that threshold, there's no going back.
Crossing the threshold into the bathroom, she paused to look at herself in the mirror with a grimace.
The Porte de France is the threshold of the ancient city.
He stopped at the threshold and asked in Russian whether Drubetskoy lived there.
If from habit and tradition he respects a stranger within his threshold, he yet considers it legitimate to warn a neighbour of the prey that is afoot, or even to overtake and plunder his guest after he has quitted his roof.