Old student’s only note is not in use any more (8)
I believe the answer is:
obsolete
'old' is the definition.
(I've seen this before)
'student's only note is not in use any more' is the wordplay.
I cannot quite see how this works, but
'only' could be 'sole' (synonyms) and 'sole' is present in the answer.
'note' could be 'te' (musical note) and 'te' is present in the answer.
'not' could be 'o' (I've seen this in other clues) and 'o' is found in the answer.
A single letter 'b' remains which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for obsolete that I've seen before include "Obese lot may be out of date" , "Disused" , "No longer useful" , "Outmoded, passe" , "Antiquated" .)