From Longman Dictionary of Contemporary Englishregicidere‧gi‧cide /ˈredʒɪsaɪd/ noun formal 1 [uncountable]SCCPGO the crime of killing a king or queen2 [countable]SCCPGO someone who kills a king or queen
Examples from the Corpus
regicide• The populists resorted to conspiracy, terror and regicide.• A daring and devious regicide or merely a clumsy archer?• Indubitable evidences of an ancient custom of ritual regicide have been found over a great portion of the globe.• His granddaughter was Dorothea Scott, a friend of several of the regicides and a Quaker pamphleteer and preacher during the 1650s.Origin regicide (1500-1600) Latin rex “king” + English -icide 