Support objection over lock (8)
I believe the answer is:
buttress
'support' is the definition.
(buttress is a kind of support)
'objection over lock' is the wordplay.
'objection' becomes 'but'.
'over' says to put letters next to each other.
'lock' becomes 'tress' (I've seen this before).
'but'+'tress'='BUTTRESS'
(Other definitions for buttress that I've seen before include "Pier" , "Support built against a wall, prop" , "Reinforce" , "strengthening side" , "She-goat" .)