Notice returning politician is wet (4)
I believe the answer is:
damp
'is wet' is the definition.
(similar in meaning)
'notice returning politician' is the wordplay.
'notice' becomes 'ad' (short for advert).
'returning' says the letters should be written in reverse.
'politician' becomes 'MP' (Member of Parliament).
'ad' back-to-front is 'da'.
'da'+'mp'='DAMP'
(Other definitions for damp that I've seen before include "dripping" , "A bit wet" , "Moisture" , "soggy" , "Slightly moist" .)