Wet two enclosures (6)
I believe the answer is:
dampen
'wet' is the definition.
(I know that dampen is a type of wet)
'two enclosures' is the wordplay.
'two enclosures' means two substitutions for 'enclosure'.
'enclosure' becomes 'dam' (I can't justify this - if you can you should give a lot more credence to this answer).
'enclosure' becomes 'pen' (pen is a kind of enclosure).
'dam'+'pen'='DAMPEN'
Can you help me to learn more?
(Other definitions for dampen that I've seen before include "Moisten" , "Discourage in moist manner" , "Make moist or depress spirit" , "Make moist (6)" , "Make slightly moist, or discourage" .)