Small bird going round a bar (6)
I believe the answer is:
saloon
'bar' is the definition.
(synonyms)
'small bird going round a' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'bird' becomes 'loon' (loon is a kind of bird).
'going round' indicates putting letters inside (some letters go around others).
's'+'loon'='sloon'
'sloon' enclosing 'a' is 'SALOON'.
(Other definitions for saloon that I've seen before include "Pub room" , "Bar or shape of car" , "An American pub, as in the wild west" , "Lounge bar" , "Large public room" .)