Grasp a small branch (4)
I believe the answer is:
twig
I believe this clue is a double definition.
'grasp' is the first definition.
(twigging is a kind of grasping)
'a small branch' is the second definition.
(I've seen this before)
(Other definitions for twig that I've seen before include "Get the idea" , "Understand; sprig" , "Latch on" , "Suddenly see - bit of a tree" , "Suddenly see; branchlet" .)