Burger bun tidbit (4)
I believe the answer is:
seed
'burger bun tidbit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for seed that I've seen before include "Tennis player; germ" , "A plant grows from it" , "Beginning; sow (land)" , "What is sown" , "Plant reproducer" .)