Forbidden to provoke in speech (7)
I believe the answer is:
illicit
'forbidden' is the definition.
(I've seen this in another clue)
'provoke in speech' is the wordplay.
'provoke' becomes 'elicit' (synonyms).
'in speech' shows a homophone (sound like).
'elicit' is a homophone of 'ILLICIT'.
'to' is the link.
(Other definitions for illicit that I've seen before include "Without approval" , "Not allowed, unlawful" , "Illegal" , "Contrary to morality or convention" , "Not lawful" .)