The bar generated air (6)
I believe the answer is:
breath
'air' is the definition.
(breath is a kind of air)
'the bar generated' is the wordplay.
'generated' indicates anagramming the letters.
'the'+'bar'='thebar'
'thebar' anagrammed gives 'BREATH'.
(Other definitions for breath that I've seen before include "Save your ...... - refrain from useless discussion" , "It is drawn all the time" , "Air received and expelled" , "Slight breeze; life" , "Slight movement of air" .)