Shiny decorative disc (6)
I believe the answer is:
sequin
'shiny decorative disc' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sequin that I've seen before include "Spangle used to decorate clothing" , "Small circular spangle for ornamenting clothing" , "Decorative spangle" , "small ornamental circle" , "Sparkling feature of ballroom dancing?" .)