Cambridge college admitting sons of old assassin (7)
I believe the answer is:
cassius
'old assassin' is the definition.
(assassin of Julius Caesar)
'cambridge college admitting sons' is the wordplay.
'cambridge college' becomes 'caius'.
'admitting' means one lot of letters goes inside another.
'sons' becomes 'ss' (I've seen this in other clues).
'caius' enclosing 'ss' is 'CASSIUS'.
'of' is the link.
(Other definitions for cassius that I've seen before include "Conspirator in Julius Caesar's murder" , "Birth name of Muhammad Ali, -- Clay" , "Conspiritor against Caesar" , "Brutus's co-conspirator (J. Caesar)" , "Conspirator in the murder of Julius Caesar" .)