Bough with top of bough spread (6)
I believe the answer is:
branch
'bough' is the definition.
(I've seen this in another clue)
'top of bough spread' is the wordplay.
'top of' says to take the initial letters.
'spread' becomes 'ranch' (synonyms).
The first letter of 'bough' is 'b'.
'b'+'ranch'='BRANCH'
'with' is the link.
(Other definitions for branch that I've seen before include "Offshoot, subsidiary part" , "Arm" , "Lateral extension of river or railway" , "Bough - offshoot - secondary office" , "division within large organisation" .)