Allows good tirades (6)
I believe the answer is:
grants
'allows' is the definition.
('grant' can be a synonym of 'allow')
'good tirades' is the wordplay.
'good' becomes 'g' (abbreviation).
'tirades' becomes 'rants' (I've seen this in other clues).
'g'+'rants'='GRANTS'
(Other definitions for grants that I've seen before include "Allows as a privilege or transfers legally" , "Agrees to, allows" , "Allows or bestows" , "Gives formally or allows as privilege" , "Donations or subsidies" .)