Set up support for Special Branch (5)
I believe the answer is:
sprig
'branch' is the definition.
(I know that sprig is a type of branch)
'set up support for special' is the wordplay.
'set up' becomes 'rig' (synonyms).
'support for' says to put letters next to each other.
'special' becomes 'sp' (abbreviation).
'rig' after 'sp' is 'SPRIG'.
(Other definitions for sprig that I've seen before include "What may be flowering" , "Small nail without a head" , "Headless nail; leafy ornament" , "Young person" , "Small stem bearing flowers" .)