Definition: to have a knife at one's throat

To be threatened. Previously, the first form of this expression was "to put a knife to someone's throat" or "to put a foot on someone's throat". The image used here is that of a man crushing his opponent with his foot as a sign of victory. The same is true of a knife held to the throat, a very threatening gesture that signifies that one is in a position of weakness. The expression has retained this meaning of being threatened.