muzzling (someone); gagging; forcing (someone) to keep quiet (about something); silencing (someone); killing (someone) to prevent them from revealing something
sealed move; next move written down and kept sealed in an envelope until the game is resumed the following day; forbidden maneuver (in sumo, martial arts, etc.); forbidden technique
incantation to rid a child of insects traditionally believed to cause disease; charm to cure colic, tantrums, etc.