Secure file may be deployed here (4)
I believe the answer is:
nail
'secure' is the definition.
(both can mean to apprehend or capture)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for nail that I've seen before include "Horny substance on finger or toe" , "A small steel wood pin" , "Hit this on the head to be dead right" , "Secure" , "A metal pin or spike" .)