Step 1: The word "Patricide" denotes the act of killing one's father. The suffix "-cide" signifies "the act of killing," and when combined with "pater" (Latin for father), it specifically refers to the killing of one's father.
Step 2: Likewise, the term "Sororicide" refers to the act of killing one's sister, with "soror" being the Latin term for sister.
This analogy highlights the link between the act of killing and the individual who is killed.
Step 3: As a result, the word associated with "Sororicide" is "Sister."
Hence, the correct answer is "Sister."