Damp fog in which nothing is visible (5)
I believe the answer is:
moist
'damp' is the definition.
(I know that damp can be written as moist)
'fog in which nothing is visible' is the wordplay.
I cannot really see how this works, but
'nothing' could be 'o' (O resembles 0) and 'o' is found within the answer.
'fog' could be 'mist' (synonyms) and 'mist' is located in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for moist that I've seen before include "Damp or clammy" , "Damp, humid" , "sloppy" , "Slightly wet, damp" , "Affected by tears, perhaps" .)