Fastened or secured with a lock; unable to be opened without a key or combination.
From Old English 'loc' meaning a fastening device, related to German 'Loch' (hole). The past participle form developed in Middle English as mechanisms became more sophisticated.
The concept of 'locking' extends far beyond physical security - we speak of being 'locked in' to contracts, having 'locked' interest rates, or even 'locked' computer screens, showing how this ancient security concept has evolved into metaphors for commitment and restriction.
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