Bombast (4)
I believe the answer is:
rant
'bombast' is the definition.
(I know that bombast can be written as rant)
This is all the clue.
(Other definitions for rant that I've seen before include "Angry outburst" , "Harangue, rave" , "Bombastically declaim" , "bombast" , "Intemperate speech" .)