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English definition of “under lock and key”

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under lock and key

locked away safely: Her jewellery is securely under lock and key at the bank. If a person, especially a criminal, is under lock and key, they are being kept in a place from which they cannot escape, usually a prison.
(Definition of under lock and key from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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SMART Thesaurus: Locking and bolting

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