Start race, say, for ingredient (4)
I believe the answer is:
sago
'start' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'race say for ingredient' is the wordplay.
'race say' becomes 'go' (racing is a kind of going).
'for' means one lot of letters go next to another (I've seen this in other clues).
'ingredient' becomes 'sa' (I can't justify this - if you can you should give a lot more credence to this answer).
'go' put after 'sa' is 'SAGO'.
Can you help me to learn more?
(Other definitions for sago that I've seen before include "Powdery starch used in cooking" , "Palm cereal" , "Type of milk pudding" , "Starchy foodstuff" , "Starchy grain used in desserts" .)