Seen in disco, 'Ronettes' sparkly top (7)
I believe the answer is:
coronet
'top' is the definition.
(type of headwear)
'seen in disco ronettes sparkly' is the wordplay.
'seen in' indicates the answer is hidden within the clue.
'CORONET' can be found hidden inside 'disco ronettes sparkly'.
(Other definitions for coronet that I've seen before include "brass embellishment" , "Simple crown" , "Jewelled headgear for peer" , "sign of rank" , "Sub-lieutenant" .)