Second figure behind is wet (7)
I believe the answer is:
moisten
'wet' is the definition.
(moistening is a kind of wetting)
'second figure behind is' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'figure' becomes 'ten' (I've seen this in other clues**).
'behind' says to put letters next to each other.
'ten' put after 'is' is 'isten'.
'mo'+'isten'='MOISTEN'
(Other definitions for moisten that I've seen before include "water a bit" , "contrary to sixteen down [DEHYDRATE]!" , "Make damp or slightly wet" , "Make damp, say lips with tongue" , "It's on me (anag)" .)