Fellows inhaling island air (4)
I believe the answer is:
mien
'air' is the definition.
(thesaurus)
'fellows inhaling island' is the wordplay.
'fellows' becomes 'men' (I've seen this before).
'inhaling' indicates putting letters inside.
'island' becomes 'i'.
'men' placed around 'i' is 'MIEN'.
(Other definitions for mien that I've seen before include "The carriage" , "A countenance like mine" , "A person's demeanour" , "Facial expression sounds miserly" , "A face - maybe mine" .)