Pass as an officer (3)
I believe the answer is:
col
I believe this clue is a double definition.
'pass' is the first definition.
(col is a term for a mountain pass)
'officer' is the second definition.
(short for colonel)
'as an' acts as a link.
(Other definitions for col that I've seen before include "Mustard" , "dip?" , "Officer" , "A depression in mountain range" , "Mountain defile" .)