Stout from barrel in bar (6)
I believe the answer is:
rotund
'stout' is the definition.
(I've seen this in another clue)
'barrel in bar' is the wordplay.
'barrel' becomes 'tun' (tun is a kind of barrel).
'in' indicates putting letters inside.
'bar' becomes 'rod' (I've seen this in another clue).
'tun' put within 'rod' is 'ROTUND'.
'from' is the link.
(Other definitions for rotund that I've seen before include "Chubby" , "Full" , "'Corpulent, round (6)'" , "Pleasantly plump or rounded" , "Bulging" .)