Bar celebration backfires (5)
I believe the answer is:
lever
'bar' is the definition.
(I know that lever is a type of bar)
'celebration backfires' is the wordplay.
'celebration' becomes 'revel' (revel is a kind of celebration).
'backfires' shows that the letters should be reversed in order (I've seen 'backfired' mean this).
'revel' written backwards gives 'LEVER'.
(Other definitions for lever that I've seen before include "Bar turning on a fulcrum" , "Rigid bar pivoted about a fulcrum" , "Lifting bar pivoted on a fulcrum" , "Means of exerting force" , "Rigid bar pivoting about a fulcrum" .)