so·ror·i·cide 
(sə-rôrĭ-sīd′, -rŏr-)
(sə-rôrĭ-sīd′, -rŏr-)n.
1. The killing of one's sister.
2. One who kills one's own sister.
[Latin soror, sister; see swesor- in the Appendix of Indo-European roots + -CIDE.]
so·ror′i·cidal (-sīdl) adj.