Still pirouetting in Montmartre nightspot (5)
I believe the answer is:
inert
'still' is the definition.
(not moving)
'pirouetting in montmartre nightspot' is the wordplay.
'pirouetting' says the letters should be written backwards (pirouette is a spin in ballet - letters spin round).
'in' indicates the answer is hidden within the clue.
'treni' is hidden within 'montmartre nightspot'.
'treni' in reverse letter order is 'INERT'.
(Other definitions for inert that I've seen before include "Unable to move or resist motion" , "(Chem.) not reactive" , "Not active or reactive" , "Inter, being unable to move" , "Chem. non-reactive" .)