Intention to keep note about criminal organisation (5)
I believe the answer is:
mafia
'criminal organisation' is the definition.
(I've seen this before)
'intention to keep note' is the wordplay.
'intention' becomes 'maia' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to keep' means one lot of letters goes inside another.
'note' becomes 'f' (musical note).
'maia' enclosing 'f' is 'MAFIA'.
'about' acts as a link.
Can you help me to learn more?
(Other definitions for mafia that I've seen before include "Sicilian criminal organisation" , "Gangsters" , "Criminal organisation also known as Cosa Nostra" , "Our family" , "Secret criminal organisation" .)