Air in the bar, circulating (6)
I believe the answer is:
breath
'air' is the definition.
(I know that breath is a type of air)
'the bar circulating' is the wordplay.
'circulating' indicates anagramming the letters.
'the'+'bar'='thebar'
'thebar' is an anagram of 'BREATH'.
'in' is the link.
(Other definitions for breath that I've seen before include "from which inspiration may be drawn" , "Air drawn in and expelled out" , "Air received and expelled" , "An inhalation and exhalation" , "Bertha (anag.)" .)