Stern's with bow (4)
I believe the answer is:
arco
'bow' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for arco that I've seen before include "Musical direction" , "Played with the bow" , "taking a bow" , "bow for players" , "which every violinist must grasp" .)