Secret remedy for alumnus? (7)
I believe the answer is:
obscure
'secret' is the definition.
(thesaurus)
'remedy for alumnus?' is the wordplay.
'remedy' becomes 'cure' (synonyms).
'for' means one lot of letters go next to another (I've seen this in other clues).
'alumnus?' becomes 'obs' (I can't justify this - if you can you should give a lot more credence to this answer).
'cure' after 'obs' is 'OBSCURE'.
(Other definitions for obscure that I've seen before include "Arcane" , "Dark - secret - inconspicuous" , "Cloudy or indistinct" , "Unknown or unclear" , "Insignificant" .)