Bun (4)
I believe the answer is:
roll
'bun' is the definition.
(I know that bun can be written as roll)
This is the entire clue.
(Other definitions for roll that I've seen before include "Gymnastic move; bread" , "Continuing success if one is on this" , "Flatten; register" , "Move on wheels - individual portion of bread" , "Eg, bap" .)