He keeps talking about balloon (6)
I believe the answer is:
gasbag
'balloon' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for gasbag that I've seen before include "Talkative person or filled balloon" , "This can be elevating" , "I talk too much" , "Prattler" , "a container of helium" .)