Graduates thus as a singer (5)
I believe the answer is:
basso
'a singer' is the definition.
(basso is a kind of singer)
'graduates thus' is the wordplay.
'graduates' becomes 'bas' (I've seen this in other clues).
'thus' becomes 'so' ('so' can be a synonym of 'thus').
'bas'+'so'='BASSO'
'as' acts as a link.
(Other definitions for basso that I've seen before include "Singer" , "low voice" , "one's deep in sound" , "Lowest male singing voice (sometimes 'profundo')" .)