Distends, expands (6)
I believe the answer is:
swells
I believe this is a double definition.
'distends' is the first definition.
('swell' can be a synonym of 'distend')
'expands' is the second definition.
(swelling is a kind of expanding)
(Other definitions for swells that I've seen before include "VIPs" , "BEcomes larger in volume, size or intensity" , "Inflates like colloquial toffs" , "Inflates like posh people" , "Becomes larger in size for posh people" .)