Something causing damp is more fluid around late evening, say (9)
I believe the answer is:
moistener
'something causing damp is more fluid' is the definition.
I can't judge whether this defines the answer.
'around late evening say' is the wordplay.
'around' means one lot of letters goes inside another.
'late evening' becomes 'ten' (I've seen this in another clue).
'say' becomes 'moiser' (I can't justify this - if you can you should give a lot more credence to this answer).
'ten' put within 'moiser' is 'MOISTENER'.
Can you help me to learn more?
(Other definitions for moistener that I've seen before include "sort of cream" , "wetter" .)