Officer must cut complete protection (7)
I believe the answer is:
shelter
'protection' is the definition.
(I know that protection can be written as shelter)
'officer must cut complete' is the wordplay.
'officer' becomes 'lt' (abbreviation for lieutenant).
'must cut' indicates putting letters inside (some letters cut their way into a word).
'complete' becomes 'sheer' (I've seen this in another clue).
'lt' placed into 'sheer' is 'SHELTER'.
(Other definitions for shelter that I've seen before include "Cover, protection" , "Refuge, protection" , "Shield as from rain" , "Place of refuge" , "Sanctuary, protection" .)