Forbidden to throw a boot (5)
I believe the answer is:
taboo
'forbidden' is the definition.
(synonyms)
'throw a boot' is the wordplay.
'throw' indicates anagramming the letters.
'a'+'boot'='aboot'
'aboot' is an anagram of 'TABOO'.
'to' is the link.
(Other definitions for taboo that I've seen before include "(Something) forbidden" , "(Irrational) prohibition" , "Socially forbidden" , "Forbidden by social custom" , "Prohibited by religion or custom" .)