Grand meal, maybe, but light (5)
I believe the answer is:
gleam
'light' is the definition.
(I have seen 'brief light' mean 'gleam' so perhaps 'light' could also mean 'gleam')
'grand meal maybe' is the wordplay.
'grand' becomes 'g' (synonyms).
'maybe' is an anagram indicator.
'meal' is an anagram of 'leam'.
'g'+'leam'='GLEAM'
'but' is the link.
(Other definitions for gleam that I've seen before include "Faint light; (quality) shine (in eyes)" , "Sparkle, glimmer" , "Flash of light" , "Shine brightly" , "shaft" .)