A stunner I fancy is moody (9)
I believe the answer is:
saturnine
'moody' is the definition.
('saturnine' can be a synonym of 'moody')
'a stunner i fancy' is the wordplay.
'fancy' indicates anagramming the letters.
'a'+'stunner'+'i'='astunneri'
'astunneri' with letters rearranged gives 'SATURNINE'.
'is' is the link.
(Other definitions for saturnine that I've seen before include "A rust nine chnage to be grave and gloomy" , "dull" , "shining? The opposite" , "dismal" , "Gloomy; dark and brooding" .)