Clamber on many a branch (5)
I believe the answer is:
climb
'clamber' is the definition.
(thesaurus)
'on many a branch' is the wordplay.
'on' says to put letters next to each other.
'many' becomes 'c' (C is the Roman numeral for 100).
'a branch' becomes 'limb' (I've seen this in another clue).
'c' put next to 'limb' is 'CLIMB'.
(Other definitions for climb that I've seen before include "Scale or clamber" , "Go up - scale" , "Get higher" , "Go higher up" , "Get a rise" .)