More moist (6)
I believe the answer is:
damper
'more moist' is the definition.
('damp' can be a synonym of 'moist')
This is the entire clue.
(Other definitions for damper that I've seen before include "Vibration reducer" , "more soppy" , "Depressive influence" , "Piano string silencer" , "Draught-regulating device" .)