A performer in taking part is terrible (7)
I believe the answer is:
Here is my best explanation:
'a performer' is the definition.
(artiste is a kind of performer)
'in taking part is terrible' is the subsidiary indication.
'in' indicates a hidden word.
'artiste' is hidden in the letters of 'taking part is terrible'.
(Other definitions for artiste that I've seen before include "A sitter for creative person", "Performers", "Performer", "Attires (anag.)", "A public performer", "Attires for professional entertainer", "Professional entertainer", "Dancer", "Professional performer" and "'Public performer, dancer or singer (7)'".)