Be less than admirable as an officer! (7)

I believe the answer is:

admiral

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'officer' is the definition.
(admiral is a kind of officer)

I can't explain the rest of the clue.

(Other definitions for admiral that I've seen before include "Navy rank" , "Naval officer of high rank" , "Senior naval officer" , "Naval chief" , "Brightly coloured butterfly" .)

I've seen this clue in the Evening Standard.

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