Arty group writhing in torment (9)
I believe the answer is:
purgatory
'torment' is the definition.
(thesaurus)
'arty group writhing' is the wordplay.
'writhing' indicates anagramming the letters.
'arty'+'group'='artygroup'
'artygroup' is an anagram of 'PURGATORY'.
'in' is the link.
(Other definitions for purgatory that I've seen before include "Mental anguish" , "Torment" , "Suffering" , "Hell on earth" .)