US lawyer on treaty blasted (8)
I believe the answer is:
attorney
'us lawyer' is the definition.
(I've seen this before)
'on treaty blasted' is the wordplay.
'blasted' indicates anagramming the letters.
'on'+'treaty'='ontreaty'
'ontreaty' with letters rearranged gives 'ATTORNEY'.
(Other definitions for attorney that I've seen before include "US lawyer" , "Legal representative" , "Person legally authorised to act for another" , "Any torte (anag.)" , "An American lawyer or barrister" .)