Inconspicuous former pupil’s remedy (7)
I believe the answer is:
obscure
'inconspicuous' is the definition.
('obscure' can be similar in meaning to 'inconspicuous')
'former pupil's remedy' is the wordplay.
'former pupil's' becomes 'obs' (abbreviation for 'Old Boy').
'remedy' becomes 'cure' ('cure' can be a synonym of 'remedy').
'obs'+'cure'='OBSCURE'
(Other definitions for obscure that I've seen before include "Not clear, hidden" , "Unheard-of" , "Hazy or indistinct" , "Like Jude, not well known" , "Dull, opaque" .)