Stick to stopping Prohibition (5)
I believe the answer is:
baton
'stick' is the definition.
(thesaurus)
'to stopping prohibition' is the wordplay.
'stopping' means one lot of letters goes inside another (stopping can mean blocking a gap).
'prohibition' becomes 'ban' (ban is a kind of prohibition).
'to' inserted into 'ban' is 'BATON'.
(Other definitions for baton that I've seen before include "A stick for a conductor and policeman" , "Conductor's rod" , "Controller of players" , "Conductor wields it - or a policeman" , "Club, stick" .)