Evening repast (6)
(Other definitions for dinner that I've seen before include "grub" , "Main meal of day" , "Repast" , "Evening meal" , "serving in 20 [MESS] ?" .)
'evening repast' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for supper that I've seen before include "Light evening meal" , "singing for this?" , "Last meal of the day" , "Early evening meal" , "Evening 2 Down" .)