Owing to some moisture, say (3)
I believe the answer is:
due
'owing' is the definition.
(similar in meaning)
'some moisture say' is the wordplay.
'some moisture' becomes 'dew' (I have seen 'Overnight moisture ' mean 'dew' so perhaps 'moisture' could also mean 'dew').
'say' shows a homophone (sound like).
'dew' sounds like 'DUE'.
'to' acts as a link.
(Other definitions for due that I've seen before include "Owing, unpaid" , "Ripe for payment or arrival" , "Entitlement" , "Expected at any moment" , "Rightful" .)