Some nasty ranting despot (6)
I believe the answer is:
tyrant
'despot' is the definition.
(I know that despot can be written as tyrant)
'some nasty ranting' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'TYRANT' can be found hidden inside 'nasty ranting'.
(Other definitions for tyrant that I've seen before include "big bully" , "Martinet" , "Despot, dictator" , "Autocrat or despot" , "Despotic ruler" .)