Work can be fun (4)
I believe the answer is:
play
I believe this clue is a double definition.
'work' is the first definition.
(I know that play is a type of work)
'fun' is the second definition.
(I know that fun can be written as play)
'can be' acts as a link.
(Other definitions for play that I've seen before include "Frolic" , "Dramatic work" , "Hamlet, for example" , "Theatrical performance" , "Freedom of movement" .)