Habitual drinker appearing in light opera (5)
I believe the answer is:
toper
'habitual drinker' is the definition.
(I've seen this before)
'in light opera' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TOPER' is hidden within 'light opera'.
'appearing' is the link.
(Other definitions for toper that I've seen before include "Soak" , "One who drinks to excess" , "Serious drinker" , "boozer" , "Lush" .)