Atmosphere in flight shunned by holy man (3)
I believe the answer is:
air
'atmosphere' is the definition.
(I know that atmosphere can be written as air)
'flight shunned by holy man' is the wordplay.
'flight' becomes 'stair' (I've seen this before).
'shunned by' indicates named letters should be taken away.
'holy man' becomes 'st' (abbreviation for saint).
'stair' with 'st' taken out is 'AIR'.
'in' acts as a link.
(Other definitions for air that I've seen before include "'Tune, melody (3)'" , "Ventilate with breathing gas" , "Broadcast; tune" , "Broadcast; gas" , "Feel" .)