Romeo's terribly gloomy (6)

I believe the answer is:

morose

'gloomy' is the definition.
(morose means gloomy or sad)

'romeo's terribly' is the wordplay.
'terribly' indicates an anagram.
'romeos' anagrammed gives 'MOROSE'.

(Other definitions for morose that I've seen before include "Sad" , "in gloomy mood" , "Glum or sour-tempered" , "Down in the dumps" , "in a grumpy mood" .)

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