Ex-pupil alone, note, and old-fashioned (8)
I believe the answer is:
obsolete
'old-fashioned' is the definition.
(thesaurus)
'ex-pupil alone note' is the wordplay.
'ex pupil' becomes 'OB' (abbreviation for 'Old Boy').
'alone' becomes 'sole' (synonyms).
'note' becomes 'te' (musical note).
'ob'+'sole'+'te'='OBSOLETE'
'and' acts as a link.
(Other definitions for obsolete that I've seen before include "Outdated" , "Out-of-date" , "Disused" , "being out of practice" , "'No longer used, out of date (8)'" .)