Lacking fresh air (6)
I believe the answer is:
stuffy
'lacking fresh air' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stuffy that I've seen before include "Close, airless" , "needing to be aired" , "Staid - airless" , "Airless - strait-laced" , "Airless or dull and narrow-minded" .)