Sauce made from tomatoes (7)
I believe the answer is:
ketchup
'sauce made from tomatoes' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ketchup that I've seen before include "Thick sauce, with tomatoes" , "Spicy tomato sauce" , "Sauce made largely of tomatoes" , "Piquant sauce, often tomato based" , "Relish" .)