Impossible Contracts
The Cyclopedic Law Dictionary · Walter A. Shumaker and George Foster Longsdorf; ed. James C. Cahill · 1922
The Cyclopedic Law Dictionary
Such contracts as cannot be performed, either because of the nature of the obligation undertaken, or because of some supervening event which renders the performance of the obligation either physically or legally impossible.
10 Am. & Eng. Enc. Law, 176.