What opens and closes safes? (3)
I believe the answer is:
ess
'what opens and closes safes?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ess that I've seen before include "Nineteenth letter" , "top secret" , "Curvaceous letter" , "Alphabet letter" , "One next to tee" .)