The Collaborative International Dictionary
Sororicide \So*ror"i*cide\ (?; 277), n. [L. 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.
Wiktionary
n. 1 The killing of one's sister. 2 A person who kills his or her sister.
Wikipedia
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 when a potent weapon is available or one is significantly older than the other and misjudges his/her own strength.
Usage examples of "sororicide".
In her name, not even matricide, parricide, fratricide, sororicide, filicide, mariticide, or other murders of near and distant kindred were wrong so long as these victims did not revere her.