Grasp small branch (4)
I believe the answer is:
twig
I believe this clue is a double definition.
'grasp' is the first definition.
(both can mean to realise something)
'small branch' is the second definition.
(I've seen this in another clue)
(Other definitions for twig that I've seen before include "Small piece of wood" , "bit of wood" , "Small shoot or branch" , "Informally grasp meaning" , "Small part of tree - suddenly understand" .)