Bar lock getting reinforcement (8)
I believe the answer is:
buttress
'reinforcement' is the definition.
(thesaurus)
'bar lock getting' is the wordplay.
'bar' becomes 'but' (both can mean 'except for').
'lock' becomes 'tress' (both can mean a piece of hair).
'getting' means one lot of letters go next to another.
'but'+'tress'='BUTTRESS'
(Other definitions for buttress that I've seen before include "It strengthens the wall" , "strengthening side" , "Wall supporter" , "Pier" , "that goes flying round the cathedral?" .)