Work for the creature with a months leave (4)
I believe the answer is:
opus
'work' is the definition.
(an opus is an artistic work)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for opus that I've seen before include "Composer's work" , "Work of 25 perhaps" , "Musical piece" , "Composition - magnum __" , "A Latin work" .)