When officer goes outside, go on (4)
I believe the answer is:
last
'go on' is the definition.
(thesaurus)
'when officer goes outside' is the wordplay.
'when' becomes 'as' (**).
'officer' becomes 'lt' (I've seen this in other clues).
'goes outside' indicates putting letters inside.
'as' inserted into 'lt' is 'LAST'.
(Other definitions for last that I've seen before include "nowhere near winning Miss World?" , "most recent model" , "Rearmost" , "Least likely" , "Shoemaker's shape" .)