Surplus actors, gloomy (8)
I believe the answer is:
overcast
'gloomy' is the definition.
(thesaurus)
'surplus actors' is the wordplay.
'surplus' becomes 'over' (I've seen this before).
'actors' becomes 'cast' (I've seen this before).
'over'+'cast'='OVERCAST'
(Other definitions for overcast that I've seen before include "(Of sky) cloudy, dull" , "Not very bright" , "The sky covered by dark clouds" , "Overacts, being gloomy" , "(Of skies) grey" .)