Oppressively hot and humid (8)
I believe the answer is:
stifling
'oppressively hot and humid' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stifling that I've seen before include "Oppressively hot and humid" , "Oppressively hot and airless" , "Flings it in suffocating manner" , "Smothering or suppressing" , "Unpleasantly hot or airless" .)