Make merry around bar (5)
I believe the answer is:
lever
'bar' is the definition.
(lever is a kind of bar)
'make merry around' is the wordplay.
'make merry' becomes 'revel' ('revel' can be a synonym of 'make merry').
'around' is a reversal indicator.
'revel' reversed gives 'LEVER'.
(Other definitions for lever that I've seen before include "Revel in moving bar" , "Machine operator" , "Revel (anag.)" , "Kind of bar for prising or lifting" , "Heavy bar" .)