The ill-tempered officer was promoted (6)

I believe the answer is:

morose

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'the ill-tempered' is the definition.
(I've seen this before)

'officer was promoted' is the wordplay.
'officer' becomes 'mo' (I am not sure about this - if you are sure you should believe this answer much more).
'was promoted' becomes 'rose' (I've seen this before).
'mo'+'rose'='MOROSE'

Can you help me to learn more?

(Other definitions for morose that I've seen before include "Sullen or glum." , "in a grumpy mood" , "Sullen, crabby" , "Silent, gloomy and ill-tempered" , "Moody, glum" .)

I've seen this clue in the Evening Standard.

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