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' indicates an anagram.
'initially' suggests taking the first letters.
'about' becomes 'c' (circa).
The first letter of 'information' is 'i'.
'posted' with letters rearranged 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" .)