a murder, however, not a killing in self-defense
The murder of a famous person or public official. President Lincoln was assassinated while attending a performance at Ford's Theatre.
when someone important is killed, often for political reasons
Assassination is the murder of a political figure or other important individual. An added distinction between assasination and other forms of killing is that an assassin usually has an ideological or political motivation, though many assassins (especially those who are not part of an organised movement) also show elements of insanity. Other motivations may be money (as in the case of a contract killing), revenge, or as a military operation.
