What is the term for the killing of a king?

The term for the killing of a king is "regicide." This word is derived from the Latin "rex," meaning king, and “cide,” a suffix meaning to kill. Regicide often carries significant historical and political implications, as the assassination of a monarch can lead to upheaval within a kingdom or nation, destabilizing political structures and leading to shifts in power.

The other options do not relate to the act of killing a king. "Redress" refers to correcting or remedying a wrong, "sardonic" describes something that is grimly mocking or cynical, and "somniferous" means inducing sleep. These definitions highlight that the context of regicide is specifically related to the act against a monarch, emphasizing its unique and serious nature in political contexts.