Stand in line with officer expressing hesitation (5)
I believe the answer is:
locum
'stand in' is the definition.
(thesaurus)
'line with officer expressing hesitation' is the wordplay.
'line' becomes 'l'.
'with' is a charade indicator (letters next to each other).
'officer' becomes 'oc' (I've seen this in other clues).
'expressing hesitation' becomes 'um' (I can't explain this - if you can you should believe this answer much more).
'l'+'oc'+'um'='LOCUM'
Can you help me to learn more?
(Other definitions for locum that I've seen before include "Stand-in medic" , "Stand-in physician" , "Person filling in" , "Professional who substitutes temporarily for another" , "Stand-in GP" .)