South African rook to eat fish (7)
I believe the answer is:
sardine
'fish' is the definition.
(sardine is a type of fish)
'south african rook to eat' is the wordplay.
'south african' becomes 'SA' (abbreviation).
'rook' becomes 'R' (chess abbreviation).
'to eat' becomes 'dine' (to dine is to eat a meal).
'sa'+'r'+'dine'='SARDINE'
(Other definitions for sardine that I've seen before include "Small pilchard" , "FRENCH FISH" , "Fish (often tinned)" , "A diner's small fish" , "Stonefish OR? Stone" .)