Excessively talkative person (7)
I believe the answer is:
windbag
'excessively talkative person' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for windbag that I've seen before include "Garrulous person" , "One spouting hot air" , "Garrulous type" , "One who speaks excessively" , "One who says a lot, but has little to say" .)