Sororicide (from Latin soror `sister` + -cide, from caedere `to cut, to kill`) is the act of killing one`s own sister. There are a number of examples of sororicide and fratricide in adolescents, even pre-adolescents, where sibling rivalry and resulting physical aggression can get out of hand and lead to the death of one of them, particularly ...
killing of one's own sister
• (n.) The murder of one`s sister; also, one who murders or kills one`s own sister.
So·ror'i·cide noun [ Latin sororocida , and sororicidium ; soror a sister + caedere to kill.] The murder of one's sister; also, one who murders or kills one's own sister. Johnson. 
Sororicide is the term for the murder of a sister.
sororicide, sororicidal 1. The murder of a sister. 2. Someone who kills his or her sister.