Prevent interception of first operative (4)
I believe the answer is:
stop
'prevent interception' is the definition.
'stop' can be an answer for 'prevent' (stopping is a kind of preventing). I'm unsure of the 'interception' bit.
'of first operative' is the wordplay.
'of' says the answer is hidden in the clue.
'STOP' is hidden within 'first operative'.
Can you help me to learn more?
(Other definitions for stop that I've seen before include "colon, say" , "high card in bridge" , "Prevent - desist" , "It could be the organist's principal" , "End or pause" .)