My only right that’s official (7)
I believe the answer is:
coroner
'that's official' is the definition.
(I've seen this before)
'my only right' is the wordplay.
'my' becomes 'cor' (both are expressions of surprise).
'only' becomes 'one' (synonyms).
'right' becomes 'r' (common abbreviation).
'cor'+'one'+'r'='CORONER'
(Other definitions for coroner that I've seen before include "Inquest officer" , "Investigator" , "One investigating death" , "Public official who conducts inquests" , "He presides over an inquest (7)" .)