Pudding ingredient (4)
I believe the answer is:
'pudding ingredient' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sago that I've seen before include "Edible powdery starch" , "Type of milk pudding" , "Powdery starchy food" , "Palm cereal" , "Starchy pudding cereal" .)