Derogatory Clause
The Cyclopedic Law Dictionary · Walter A. Shumaker and George Foster Longsdorf; ed. James C. Cahill · 1922
The Cyclopedic Law Dictionary
In a will, this is a sentence or secret character inserted by the testator, of which he reserves the knowledge to himself, with a condition that no will he may make thereafter should be valid, unless this clause be inserted word for word. This is done as a precaution to guard against later wills being extorted by violence, or otherwise improperly obtained. By the law of England such a clause would be void, as tending to make the will irrevocable.
Wharton.