Dictator's heartless attempt to deliver a tirade (6)
I believe the answer is:
tyrant
'dictator's' is the definition.
(tyrant is a kind of dictator)
'heartless attempt to deliver a tirade' is the wordplay.
'heartless' says to hollow out the word (remove centre letters).
'attempt' becomes 'try' (synonyms).
'to deliver a tirade' becomes 'rant' (a tirade is a rant).
'try' with its middle taken out is 'ty'.
'ty'+'rant'='TYRANT'
(Other definitions for tyrant that I've seen before include "Authoritarian" , "Oppressive and cruel ruler" , "Despotic ruler" , "taskmaster" , "Person dictating" .)