Tyrant posted abroad (6)
I believe the answer is:
despot
'tyrant' is the definition.
(I know that tyrant can be written as despot)
'posted abroad' is the wordplay.
'abroad' indicates an anagram.
'posted' is an anagram of 'DESPOT'.
(Other definitions for despot that I've seen before include "Caesar for one" , "One exploiting rule" , "Gaddafi, say" , "Autocrat" , "Cruel and oppressive dictator" .)