Mike and I leave Belgium drifting in balloon (5)
I believe the answer is:
bulge
'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 bulge that I've seen before include "Swelling - sudden increase" , "Hump" , "Battle of the -----: last major German counter-offensive of WWII (1944)" , "Rounded swelling" , "Protuberance or outward swelling" .)