Main charity sent back something sparkling (6)
I believe the answer is:
diadem
'something sparkling' is the definition.
'main charity sent back' is the wordplay.
'main' becomes 'med' ('main' can mean the sea - eg Mediterranean or Med).
'charity' becomes 'aid' (eg foreign aid).
'sent back' shows that the letters should be reversed in order.
'med'+'aid'='medaid'
'medaid' backwards is 'DIADEM'.
(Other definitions for diadem that I've seen before include "A crowning glory" , "Crown or headband worn as symbol of sovereignty" , "Regal power" , "Ornamental jewelled headdress" , "Kingly crown" .)