Stun with a stone (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
rock
I believe this is a double definition.
'stun' is the first definition.
(thesaurus)
'a stone' is the second definition.
('rock' can be a synonym of 'stone')
'with' is the link.
(Other definitions for rock that I've seen before include "Edinburgh - -" , "Swing" , "Move side to side" , "Sway - very big stone" , "Music; diamond" .)