Complete a tirade about Republican (6)
I believe the answer is:
arrant
'complete' is the definition.
(thesaurus)
'a tirade about republican' is the wordplay.
'tirade' becomes 'rant' (I've seen this before).
'about' is a charade indicator (letters next to each other).
'republican' becomes 'r' (abbreviation).
'rant' after 'r' is 'rrant'.
'a'+'rrant'='ARRANT'
(Other definitions for arrant that I've seen before include "Out-and-out, utter" , "Complete (nonsense)" , "'Complete, stark (6)'" , "Rat ran badly and became unmitigated" , "Utter and absolute, maybe nonsense" .)