From cellist, 'Les Sylphides' is sluggish (8)
I believe the answer is:
listless
'sluggish' is the definition.
(I've seen this in another clue)
'from cellist les sylphides' is the wordplay.
'from' indicates a hidden word.
'LISTLESS' can be found hidden inside 'cellist les sylphides'.
'is' acts as a link.
(Other definitions for listless that I've seen before include "Low-spirited" , "(unlike Ko-Ko)" , "Short of energy (and ill-equipped for shopping?)" , "Tells sis to be lacking in energy" , "Lacking enthusiasm or energy" .)