Posted wrong information initially about authoritarian (8)
I believe the answer is:
despotic
'authoritarian' is the definition.
(synonyms)
'posted wrong information initially about' is the wordplay.
'wrong' is an anagram indicator.
'initially' indicates taking the first letters.
'about' becomes 'c' (abbreviation for circa).
The initial letter of 'information' is 'i'.
'posted' anagrammed gives 'despot'.
'despot'+'i'+'c'='DESPOTIC'
(Other definitions for despotic that I've seen before include "of tyrant" , "'Cruel and oppressive, as a dictator (8)'" , "Autocratic" , "Referring to absolute power" , "Dictatorial" .)