With the bow, in music (4)
I believe the answer is:
arco
'with the bow in music' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for arco that I've seen before include "Played with the bow" , "bow for players" , "taking a bow" , "Musical direction" , "which every violinist must grasp" .)