Traitor has new tirade (4)
I believe the answer is:
rant
'tirade' is the definition.
(I've seen this before)
'traitor has new' is the wordplay.
'traitor' becomes 'rat' (I've seen this before).
'has' indicates putting letters inside.
'new' becomes 'n'.
'rat' enclosing 'n' is 'RANT'.
(Other definitions for rant that I've seen before include "Bombastically declaim" , "Shout wildly at length" , "Speak intemperately" , "bombast" , "Talk wildly or violently" .)