Almost all university students — about 1000 — graduate (7)
I believe the answer is:
alumnus
'graduate' is the definition.
(synonyms)
'almost all university students about 1000' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'university' becomes 'U' (abbreviation for university).
'students' becomes 'nus' (National Union of Students).
'about' is a charade indicator (letters next to each other).
'n000' becomes 'M' (Roman numeral).
'all' with its last letter taken away is 'al'.
'nus' put after 'm' is 'mnus'.
'al'+'u'+'mnus'='ALUMNUS'
(Other definitions for alumnus that I've seen before include "Former pupil or student" , "(US) college graduate" , "School or college graduate" , "Past pupil" , "Old pupil" .)