Unpleasantly humid (6)
I believe the answer is:
clammy
'unpleasantly humid' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for clammy that I've seen before include "Unpleasantly sticky and moist" , "Wet and sticky" , "Stewing" , "Unpleasantly cool and humid" , "Moist and adhesive" .)