Double locks in attempt to secure new file (4)
I believe the answer is:
Here is my best explanation:
'double locks in attempt' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'to secure new file' is the wordplay.
'to secure' indicates putting letters inside.
'new' becomes 'n'.
'file' becomes 'rig' (I can't justify this - if you can you should give a lot more credence to this answer).
'n' put within 'rig' is 'RING'.
(Other definitions for ring that I've seen before include "Surround; reverberate", "Sound a doorbell", "Band - call", "Contact", "Form circle around", "Arena; jewellery item", "sign of union?", "It's carried by Frodo", "Phone; circular band" and "Hoop".)