Makeshift bar opening (7)
I believe the answer is:
stopgap
'makeshift' is the definition.
(I know that makeshift can be written as stopgap)
'bar opening' is the wordplay.
'bar' becomes 'stop' (bar can mean to stop or prevent).
'opening' becomes 'gap' (synonyms).
'stop'+'gap'='STOPGAP'
(Other definitions for stopgap that I've seen before include "Interim" , "Temporary fix" , "A temporary substitute or solution" , "Temporary measure" , "caretaker" .)