sealed move

British  

noun

1. chess the last move before an adjournment, which is written down by the player making it, sealed in an envelope, and kept secret from his opponent until play is resumed

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Example Sentences

White resigned after Black’s sealed move of 41 … Bd3+, having no need to see lines like 42.

From Washington Times • Aug. 30, 2022

Yet he still might have drawn the game with a better sealed move before adjournment.

From Time Magazine Archive

Upon the resumption of an adjourned game the position existing at the time of adjournment shall be set up and the sealed move made on the board.

From The Blue Book of Chess Teaching the Rudiments of the Game, and Giving an Analysis of All the Recognized Openings by Staunton, Howard