Second wine is fun (5)
I believe the answer is:
sport
'fun' is the definition.
(I know that fun can be written as sport)
'second wine' is the wordplay.
'second' becomes 's' (common abbreviation).
'wine' becomes 'port' (port is a kind of wine).
's'+'port'='SPORT'
'is' acts as a link.
(Other definitions for sport that I've seen before include "Game; display" , "Eg, cricket" , "Recreation, play" , "Eg, rugby" , "Wear - game - generous type" .)