Concerning earlier banquet (6)
I believe the answer is:
'banquet' is the definition.
(I've seen this in another clue)
'concerning earlier' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'earlier' becomes 'past' (I've seen this in another clue).
(Other definitions for repast that I've seen before include "Banquet" , "Food - tapers (anag)" , "Something to eat" , "A formal sort of meal" , "Feast, meal" .)