Ambition to swallow stout grew (8)
I believe the answer is:
enlarged
'grew' is the definition.
(enlarging is a kind of growing)
'ambition to swallow stout' is the wordplay.
'ambition' becomes 'end' ('end' can mean a goal or purpose).
'to swallow' indicates putting letters inside.
'stout' becomes 'large' (I've seen this before).
'end' going around 'large' is 'ENLARGED'.
(Other definitions for enlarged that I've seen before include "Made greater" , "Magnified" , "puffed out?" , "Made bigger, say photo" , "Made bigger like photo" .)