A bit of grammar and vocabulary:

The Punctuation Game via fortysomething.

Sororicide
SYLLABICATION: so·ror·i·cide
PRONUNCIATION: AUDIO: s-rôr-sd, -rr- KEY
NOUN: 1. The killing of one’s sister.
2. One who kills one’s own sister.
ETYMOLOGY: Latin soror, sister; see swesor- in Appendix I + –cide.
OTHER FORMS: so·rori·cidal (-sdl) —ADJECTIVE

Another way to define this word: that which will happen when older sister discovers that younger sister borrowed her jean jacket and now cannot find it – younger sister suspects, but is not sure, that she left it at another’s house after a sleep over.