Just kidding - refuse (5)
I believe the answer is:
chaff
This clue could be a double definition.
'just kidding' is the first definition.
'chaff' can be an answer for 'kidding' (thesaurus). I am not certain of the 'just' bit.
'refuse' is the second definition.
(I've seen this in another clue)
Can you help me to learn more?
(Other definitions for chaff that I've seen before include "Worthless material (from corn)" , "Corn-husks separated from the grain" , "It's separated from wheat during threshing" , "Refuse - banter" , "something worth little" .)