Tyrannicide literally means the killing of a tyrant. Typically, the term is taken to mean the killing or assassination of tyrants for the common good. The term "tyrannicide" does not apply to tyrants killed in battle or killed by an enemy in an armed conflict. It is rarely applied when a tyrant is killed by a person acting for selfish reasons, such as to take power for themselves, or to the killing of a former tyrant. Sometimes, the term is restricted to killings undertaken by people who are actually subject to the tyrant. The term is also used to denote those who actually commit the act of killing a tyrant: ie, Harmodius and Aristogeiton are called 'the tyrannicides'.
Tyrannicide can also be a political theory. The Monarchomachs in particular developed a theory of tyrannicide, with Juan de Mariana describing their views in the 1598 work De rege et regis institutione.] The Jesuistic casuistry developed a similar theory, criticized by Blaise Pascal in the Provincial Letters.[citation