mortise lock 
noun
A lock which is set within the body of a door in a recess or mortise, as opposed to one attached to the door surface.I am replacing an old mortise lock - the skeleton key style one - with a new mortise lock....
- The large sash windows of his 100-year-old home were fitted with bolts, and a mortise lock and a spy hole were fitted in his front door.
- This pattern was created to operate and decorate a mortise lock whose mechanism was built into the fabric of the door.
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