Turning up, make merry in bar (5)
I believe the answer is:
lever
'bar' is the definition.
(I know that lever is a type of bar)
'turning up make merry' is the wordplay.
'turning up' says the letters should be written backwards.
'make merry' becomes 'revel' (synonyms).
'revel' back-to-front is 'LEVER'.
'in' is the link.
(Other definitions for lever that I've seen before include "Purchase from bar" , "Bar operating machinery" , "Heavy bar" , "Rigid bar pivoting about a fulcrum" , "Lifting bar pivoted on a fulcrum" .)