• (a.) Pertaining to regicide, or to one committing it; having the nature of, or resembling, regicide.
Reg'i·ci`dal adjective Pertaining to regicide, or to one committing it; having the nature of, or resembling, regicide. Bp. Warburton. 
regicide, regicidism, regicidal 1. The killing of a king; especially, someone who kills his/her own king. 2. Someone who commits the crime of regicide.