Flag officer (6)
I believe the answer is:
ensign
This clue is a double definition.
'flag' is the first definition.
(ensign is a kind of flag)
'officer' is the second definition.
(I've seen this before)
(Other definitions for ensign that I've seen before include "Flag - officer, formerly" , "US naval rank" , "Ship's flag and junior officer" , "Look upon with contempt" , "Ship's flag to show nationality" .)