Left-winger, but not a wet (5)
I believe the answer is:
moist
'wet' is the definition.
(similar in meaning)
'left-winger but not a' is the wordplay.
'left-winger' becomes 'maoist' (follower of Mao Tse-Tung).
'but not' suggests deleting specific letters.
'maoist' with 'a' taken away is 'MOIST'.
(Other definitions for moist that I've seen before include "Affected by tears, perhaps" , "Damp or clammy" , "sloppy" , "lubricated" , "Damp, humid" .)