Forbidden, thanks to cry of disapproval (5)
I believe the answer is:
taboo
'forbidden' is the definition.
(synonyms)
'thanks to cry of disapproval' is the wordplay.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'to cry of disapproval' becomes 'boo' (I've seen this before).
'ta'+'boo'='TABOO'
(Other definitions for taboo that I've seen before include "Anathema" , "Not permitted" , "By religion or custom, not to be done or touched" , "A ban or prohibition of superstitious kind" , "Strictly forbidden" .)