Treat furs crumpled in foil (9)
I believe the answer is:
frustrate
'foil' is the definition.
(synonyms)
'treat furs crumpled' is the wordplay.
'crumpled' indicates an anagram.
'treat'+'furs'='treatfurs'
'treatfurs' with letters rearranged gives 'FRUSTRATE'.
'in' is the link.
(Other definitions for frustrate that I've seen before include "Put a stop to" , "'Thwart, disappoint (9)'" , "Deprive of hope" , "Prevent (plan) from being fulfilled" , "Prevent from progressing" .)