Small offshoot (4)
I believe the answer is:
twig
'small offshoot' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for twig that I've seen before include "A small branch - cop on?" , "small piece in plane, say" , "Small part of tree - suddenly understand" , "Eventually grasp" , "Finally understand" .)