Second drink for fun (5)
I believe the answer is:
sport
'fun' is the definition.
('sport' can be a synonym of 'fun')
'second drink' is the wordplay.
'second' becomes 's' (common abbreviation).
'drink' becomes 'port' (port is a kind of drink).
's'+'port'='SPORT'
'for' acts as a link.
(Other definitions for sport that I've seen before include "Recreation, play" , "Physical recreation" , "Eg, rugby" , "Games" , "Game; display" .)