Prominent former pupil with strange virtues (9)
I believe the answer is:
obtrusive
'prominent' is the definition.
(I've seen this before)
'former pupil with strange virtues' is the wordplay.
'former pupil' becomes 'OB' (abbreviation for 'Old Boy').
'with' says to put letters next to each other.
'strange' is an anagram indicator.
'virtues' anagrammed gives 'trusive'.
'ob'+'trusive'='OBTRUSIVE'
(Other definitions for obtrusive that I've seen before include "Unpleasantly noticeable or prominent" , "Annoyingly noticeable" , "Unwelcomely prominent" , "Pushing - forward" , "Over-prominent" .)