£50 notes held in lawful fashion (5)
I believe the answer is:
legal
'held in lawful fashion' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives can occasionally define each other.
'ps50 notes' is the wordplay.
I cannot really understand how this works, but
'notes' could be 'ga' (two musical notes) and 'ga' is found 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 legal that I've seen before include "Legitimate" , "Within bounds of law" , "Constitutional" , "In accordance with law" , "Referring to the law" .)