Capricious, mercurial (6)
I believe the answer is:
fickle
I believe this clue is a double definition.
'capricious' is the first definition.
(I've seen this in another clue)
'mercurial' is the second definition.
(I've seen this in another clue)
(Other definitions for fickle that I've seen before include "Often changing, not reliable emotionally" , "Erratic, unpredictable" , "Inconstant, changeable" , "Changeable, capricious" , "Liable to sudden unpredictable change" .)