Rut (6)
I believe the answer is:
groove
'rut' is the definition.
(I know that rut can be written as groove)
This is all the clue.
(Other definitions for groove that I've seen before include "Long narrow cut or depression" , "Long narrow channel or kind of rut" , "Long narrow channel in surface of hard material" , "Long narrow channel in hard material, say record" , "'Channel, furrow (6)'" .)