A lesson lacking guidelines (6)

I believe the answer is:

amoral

I'm a little stuck... Click here to teach me more about this clue!

'a lesson lacking guidelines' is the definition.
I can't tell whether this definition defines the answer.

'a lesson' is the wordplay.
'lesson' becomes 'moral' (as in the moral of the story).
'a'+'moral'='AMORAL'

Can you help me to learn more?

(Other definitions for amoral that I've seen before include "Without ethics" , "without guiding principles" , "outrageous!" , "Having no code of ethics" , "Unethical" .)

I've seen this clue in The Mirror.

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