Grasp the branch (4)
I believe the answer is:
twig
I believe this is a double definition.
'grasp' is the first definition.
(both can mean to realise something)
'branch' is the second definition.
(I know that twig is a type of branch)
'the' is the link.
(Other definitions for twig that I've seen before include "bit of wood" , "Slender woody shoot" , "Division of branch" , "very little from box, perhaps" , "Suddenly comprehend" .)