Empty or boastful talk (3,3)
I believe the answer is:
hot air
'empty or boastful talk' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for hot air that I've seen before include "Bombast or balloon filler" , "Gas" , "Boastful talk or balloon filling" , "Empty or boastful talk - good for balloons" , "Guff" .)