Officer without company entering pass (7)
I believe the answer is:
colonel
'officer' is the definition.
(colonel is a kind of officer)
'without company entering pass' is the wordplay.
'without company' becomes 'lone' (lonely).
'entering' means one lot of letters goes inside another.
'pass' becomes 'col' (col is a term for a mountain pass).
'lone' inserted within 'col' is 'COLONEL'.
(Other definitions for colonel that I've seen before include "Bogey perhaps" , "Commissioned officer" , "Commander" , "Army rank" , "Comissioned military officer" .)