Merrymaking in back bar (5)
I believe the answer is:
revel
'merrymaking' is the definition.
(revel is a kind of merrymaking)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for revel that I've seen before include "Make merry, have a ball" , "Take great pleasure" , "Be festive, enjoy" , "Celebrate noisily" , "Have a few drinks etc." .)