A type of door latch with a bolt that cannot be retracted from the outside without a key, providing security against lock bumping.
From 'dead' (unable to move, fixed) plus 'latch' (a fastening mechanism). 'Dead' here means the bolt is mechanically locked and cannot move, combining with 'latch' from Old English 'læccan' (to seize).
The deadlatch was invented to prevent burglars from bumping locks—a technique where you tap a specially cut key to shock the pins into alignment—making it a response to an old security weakness.
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