Capricious desire (4)
I believe the answer is:
whim
'capricious desire' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for whim that I've seen before include "Fancy, notion" , "Impulse or caprice" , "fantastic creation from the past" , "Sudden impulse" , "Sudden odd desire" .)