Catch on small branch of tree (4)
I believe the answer is:
twig
'catch on' is the definition.
(synonyms)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for twig that I've seen before include "Cotton on - small branch" , "Get the idea" , "Eventually grasp" , "small piece in plane, say" , "Suddenly comprehend" .)