Old student in compound before sunup (7)
I believe the answer is:
alumnus
'old student' is the definition.
(eg former student of a university)
'compound before sunup' is the wordplay.
'compound' becomes 'alum' (chemical compound).
'before' is a charade indicator (letters next to each other).
'sunup' becomes 'nus' ('sun' written backwards or up).
'alum'+'nus'='ALUMNUS'
'in' is the link.
(Other definitions for alumnus that I've seen before include "Old pupil" , "Former college pupil" , "(US) college graduate" , "Past pupil" , "School or college graduate" .)