Fable's message (5)
I believe the answer is:
moral
'fable's message' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for moral that I've seen before include "ethical principle" , "Relating to good and evil" , "Honourable" , "Pertaining to right and wrong conduct" , "Practical lesson to be drawn from an experience" .)