Swan Lake or Coppelia, say (6)
I believe the answer is:
ballet
This clue is a double definition.
'swan lake' is the first definition.
(I've seen this in another clue)
'coppelia say' is the second definition.
(I know that Copplia is a ballet)
(Other definitions for ballet that I've seen before include "Classical dance form" , "The Nutcracker or Giselle, say" , "Artistic dance form" , "Eg, Swan Lake" , "Theatrical dance" .)