Humid, close (5)
I believe the answer is:
muggy
This clue is a double definition.
'humid' is the first definition.
(muggy can mean humid or close)
'close' is the second definition.
(I've seen this before)
(Other definitions for muggy that I've seen before include "Oppressively humid" , "Damp and stifling" , "Unpleasantly humid" , "Warm and wet" , "Warm and humid" .)