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TAKE THE QUIZ“lock and ?”
The following 2 entries include the term lock and ?.
lock-and-block system
noun: a railway block system in which the signals permitting a train to enter a block are locked while a train is in the block and automatically unlocked as it leaves the block
under lock and key
phrase: in a room, box, etc., that is locked
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Merriam-Webster unabridged
