An objection to neighbour (4)
I believe the answer is:
abut
'neighbour' is the definition.
(I've seen this before)
'an objection' is the wordplay.
'an' becomes 'a'.
'objection' becomes 'but'.
'a'+'but'='ABUT'
'to' is the link.
(Other definitions for abut that I've seen before include "Touch (side of next building)" , "Adjoin, touch" , "Neighbour" , "Touch upon" , "Lie adjacent to" .)