Morose nun's irate for a change (9)
I believe the answer is:
saturnine
'morose' is the definition.
('saturnine' can be a synonym of 'morose')
'nun's irate for a change' is the wordplay.
'for a change' indicates an anagram.
'nuns'+'irate'='nunsirate'
'nunsirate' is an anagram of 'SATURNINE'.
(Other definitions for saturnine that I've seen before include "Turn in sea makes one gloomy" , "may be brooding" , "dismal" , "A rust nine chnage to be grave and gloomy" , "Gloomy; dark and brooding" .)