I believe the answer is:
'dampen' is the definition.
(I know that dampen can be written as moisten)
This is the entire clue.
(Other definitions for moisten that I've seen before include "contrary to sixteen down [DEHYDRATE]!" , "Add water - dampen" , "It's on me (anag)" , "water a bit" , "Make damp, say lips with tongue" .)