deadbolt

Short definition from Wiktionary

Noun

1. 1
   The part of the lock which is moved when the key is engaged.
2. 2
   A kind of lock in which the bolt (moving portion) is held in position by the cylinder rather than by a spring and so cannot be retracted except by turning the cylinder.

Verb

1. 1
   To fasten or secure with a deadbolt.