Endless hard tirade, notorious (6)
I believe the answer is:
arrant
'notorious' is the definition.
(I've seen this before)
'endless hard tirade' is the wordplay.
'endless' means to look at the middle letters.
'tirade' becomes 'rant' (both can mean an angry outburst).
The middle letters of 'hard' are 'ar'.
'ar'+'rant'='ARRANT'
(Other definitions for arrant that I've seen before include "Complete (nonsense)" , "Downright, out-and-out - say nonsense" , "Downright - notorious" , "Utter; downright" , "'Complete, stark (6)'" .)