Fury's beginning to swell after punch that's light (8)
I believe the answer is:
flambeau
'that's light' is the definition.
(flambeau is a kind of light)
'fury's beginning to swell after punch' is the wordplay.
'beginning to' says to take the initial letters.
'swell' becomes 'beau' (synonyms).
'after' says to put letters next to each other.
'punch' becomes 'lam' (lam can mean to hit).
The first letter of 'furys' is 'f'.
'beau' put after 'lam' is 'lambeau'.
'f'+'lambeau'='FLAMBEAU'
(Other definitions for flambeau that I've seen before include "Flaming torch" , "Burning torch" , "One may be burning" , "Old blazer" , "Torch; candlestick" .)