Revolutionary skill taking care of excellent item of jewellery (5)
I believe the answer is:
tiara
'item of jewellery' is the definition.
(I've seen this before)
'revolutionary skill taking care of excellent' is the wordplay.
'revolutionary' is a reversal indicator.
'skill' becomes 'art' (I've seen this before).
'taking care of' indicates putting letters inside.
'excellent' becomes 'ai'.
'art' going around 'ai' is 'arait'.
'arait' reversed gives 'TIARA'.
(Other definitions for tiara that I've seen before include "Jewelled head ornament" , "Great delight" , "Jewelled headpiece" , "High diadem" , "Decorative headgear" .)