Definition
The killing of a monarch or sovereign ruler. The term carries two senses that historical legal dictionaries treat as inseparable: (1) the act itself — the murder of a reigning sovereign — and (2) the person who commits or participates in such killing. As both Black's editions and Rapalje & Lawrence record, "regicide" names both the crime and the criminal.
As a legal category, regicide is not a standalone offense in modern common law systems. It is prosecuted under ordinary homicide or murder statutes, sometimes with aggravating circumstances tied to the victim's status. Its legal significance has historically been more constitutional and political than penal — the act dissolves a reign, can trigger succession crises, and in earlier legal thought was treated as a species of treason rather than simple homicide.
Common Language
Modern common usage (Wiktionary): "The killing of a king."
Historical common usage (Webster's 1913): "One who kills or who murders a king; specifically (Eng. Hist.), one of the judges who condemned Charles I. to death. The killing or the murder of a king."
The gap between common and legal meaning is narrow but worth noting. Ordinary usage focuses on the act. Legal usage, as reflected uniformly across the historical dictionaries, doubles the term — it covers both the deed and the doer. Webster's 1913 entry preserves the historically specific English usage referring to the parliamentary judges of Charles I, a sense that had no formal legal counterpart in the common law of crimes but carried enormous constitutional weight in the development of English public law.
Common Confusion
Regicide is frequently conflated with treason in historical legal sources, and the conflation is not merely careless. Under English law, the killing of the king was constructively an act of high treason under the Treason Act 1351, not a separate offense called regicide. The term "regicide" thus describes the act by reference to the victim's identity, while "treason" describes it by reference to the perpetrator's duty of allegiance. A researcher treating the two as synonymous will miss this structural distinction: not all treason is regicide, and historically, regicide was prosecuted as treason, not as a crime bearing its own name in the indictment.
Why It Matters in Research
Researchers will rarely find "regicide" as a charge in case law or statute. It functions in legal literature as a descriptive and classificatory term rather than an operative one. Several navigational points apply:
First, in historical English sources, regicide prosecutions appear under treason, not homicide or any charge using the word regicide itself. Searching for the term in case reporters or indictment records will return limited results; searching under high treason will return the substantive material.
Second, the dual meaning — act and actor — requires attention when reading historical legal texts. A passage stating that "the regicides were punished" refers to persons; a passage on "the crime of regicide" refers to the act. Context usually clarifies, but the ambiguity is real and present in original sources.
Third, Anderson's Dictionary of Law cross-references regicide to homicide rather than treason, which signals the nineteenth-century American legal understanding: without a monarchy, regicide had no practical domestic application and was absorbed into general homicide taxonomy. This matters for researchers using American legal materials — the term appears in comparative, historical, and international law contexts, not in domestic criminal law doctrine.
Fourth, in international law and comparative constitutional law contexts, regicide takes on additional dimensions. The killing of a head of state has been addressed in extradition treaties and the "attentat clause" — a provision, originating in Belgian treaty practice after the 1854 attempt on Napoleon III, excluding political assassinations of heads of state from the political offense exception to extradition. Researchers working in extradition law or international criminal law should connect regicide to that doctrine.
Fifth, the Rapalje & Lawrence entry appends a note on the French law term "régime" immediately after defining regicide — an artifact of alphabetical proximity, not legal connection. Researchers using that source should not infer any substantive linkage.
Historical Dictionary Support
The four source dictionaries show near-total agreement on the core definition. Black's (both editions) and Rapalje & Lawrence give identical or near-identical language: murder of a sovereign, plus the person who commits it. Anderson's Dictionary of Law declines to define the term independently and redirects to homicide, which reflects a characteristically practical American approach — without a sovereign to kill, the term is taxonomically a subset of murder, nothing more.
None of the historical sources address the treason dimension, the attentat clause, or the constitutional significance of regicide in succession law. For those threads, researchers must go beyond the legal dictionaries to constitutional history, international law treatises, and comparative sources. The silence of the dictionaries on these points is itself informative: by the time these volumes were compiled, regicide was a term of historical and comparative interest in American law, not an active category of domestic doctrine.
Webster's 1913 provides the most contextually rich entry of any source here, preserving the specific English historical reference to the Cromwellian judges — a sense absent from every legal dictionary consulted. That specificity is valuable for researchers working on seventeenth-century English constitutional history.
Jurisdictional Note
In modern common law jurisdictions with constitutional monarchies (United Kingdom, Commonwealth realms), the killing of the sovereign remains prosecutable as treason under statutory treason law, not under any offense named regicide. In republican systems, equivalent conduct — killing a head of state — is prosecuted under aggravated murder or, where applicable, specific statutes protecting heads of state. No modern jurisdiction maintains a standalone offense of regicide by that name.