Judicial rule.

[Escutcheon]

What is the rule barring one from denying truth from something that has already been settled please?

[novalis]

estoppel
You would have been better off putting this in Quizzes & Puzzles/Crosswords as it was a crossword clue last weekend.

[Escutcheon]

Thanks. I realised that it was estoppel minutes after you had posted your answer! I needed it for a legal case I'm involved in. Which puzzle was this? (I live in France).

[novalis]

Hi - Just seen your reply. It was one of the Telegraph GK crosswords last weekend. That's what made me think you were doing that puzzle.