Jeer at substitute (4)
I believe the answer is:
mock
I believe this clue is a double definition.
'jeer at' is the first definition.
(thesaurus)
'substitute' is the second definition.
(thesaurus)
(Other definitions for mock that I've seen before include "cod" , "Scoff at" , "Imitation; tease scornfully" , "Tease or laugh at" , "Tease - fake" .)