Promise to repay accepted by a class outraged about lustful behaviour (9)
I believe the answer is:
salacious
'outraged about lustful behaviour' is the definition.
The answer and definition are not the same part of speech. However, adjectives and past participle verbs can sometimes mean the same thing.
'promise to repay accepted by a class' is the wordplay.
I cannot really understand how this works, but
'promise' could be 'iou' (I owe you, a promise to pay a debt) and 'iou' is located in the answer.
'accepted' could be 'a' (financial abbreviation) and 'a' is present in the answer.
'a' is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for salacious that I've seen before include "Arousing lustful feelings" , "Prurient, bawdy" , "Lewd" , "Risque" , "Arousing lustful thoughts" .)