sororicide

from The Collaborative International Dictionary of English v.0.48
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.
   [1913 Webster]
    

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