Work for fun (4)
I believe the answer is:
play
I believe this is a double definition.
'work' is the first definition.
(I know that work can be written as play)
'fun' is the second definition.
(I know that fun can be written as play)
'for' is the link.
(Other definitions for play that I've seen before include "Portray in a drama" , "Drama - latitude - sport" , "Make sport" , "Scope - entertainment" , "Stage work" .)