Tiara got damaged by incendiary (8)
I believe the answer is:
agitator
'incendiary' is the definition.
(thesaurus)
'tiara got damaged' is the wordplay.
'damaged' indicates an anagram.
'tiara'+'got'='tiaragot'
'tiaragot' is an anagram of 'AGITATOR'.
'by' is the link.
(Other definitions for agitator that I've seen before include "One causing trouble" , "Person who stirs up trouble" , "One fomenting trouble" , "washing machine" , "Demagogue" .)