Powerful novel? It unsettled (7)
I believe the answer is:
violent
'powerful' is the definition.
(thesaurus)
'novel? it unsettled' is the wordplay.
'unsettled' is an anagram indicator.
'novel'+'it'='novelit'
'novelit' anagrammed gives 'VIOLENT'.
(Other definitions for violent that I've seen before include "Sharp" , "Intensely forcible" , "Vehement; unrestrained" , "Hot-headed" , "Using extreme physical force" .)