Returning the cakes would be an insult (4)
I believe the answer is:
buns
'insult' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for buns that I've seen before include "Food items" , "Cakes" , "Small rolls" .)