Smooth routine (6)
I believe the answer is:
groove
'smooth routine' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for groove that I've seen before include "Spiral cut on gramophone disc" , "Rut - routine" , "Long narrow cut or depression" , "Long thin channel in surface of hard material" , "Long shallow indentation" .)