Clue to answer (3)
I believe the answer is:
key
(Other definitions for key that I've seen before include "Crucial arch-stone" , "Vital" , "Lock undoer" , "Device for lock" , "locker" .)
I believe the answer is:
key
(Other definitions for key that I've seen before include "Crucial arch-stone" , "Vital" , "Lock undoer" , "Device for lock" , "locker" .)