1963 assassin (6)
I believe the answer is:
'1963 assassin' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oswald that I've seen before include "Lee Harvey -, accused J. F. Kennedy assassin" , "Lee Harvey --, killer of J. F. Kennedy" , "Lee Harvey ---, president Kennedy's killer" , "King of the Northumbrians, d. 642 - President Kennedy's assassin, d. 1963" , "Lee Harvey . . . . . . assassinated J F Kennedy" .)