In the following question, choose the one-word substitute for the given phrase: Killing of one's own child.

Introduction / Context:
This question is about one-word substitution, a frequent topic in English vocabulary sections of competitive exams. The phrase given relates to the act of killing one's own child. Many English words for killing are formed with the suffix cide, which means killing or act of killing. Understanding the roots of such words helps candidates select the exact term that fits the given definition.

Given Data / Assumptions:
- Phrase: Killing of one's own child.
- Options: Foeticide, Filicide, Infanticide, Lupicide.
- We must choose the single word that accurately describes this act.
- The context is vocabulary related to types of killing, often used in legal, medical or ethical discussions.

Concept / Approach:
The root fili or filius in Latin refers to a son or child, while fetic or foetic refers to a fetus. Infans in Latin refers to a very young baby, and lupus means wolf. Therefore, the word Filicide literally means killing of one's own son or daughter. Foeticide means killing of a fetus, for example during an illegal procedure. Infanticide is killing of an infant or very young baby, and Lupicide is killing of a wolf. The phrase in the question specifically mentions one's own child, not a fetus or a particular animal, so Filicide is the most accurate term.

Step-by-Step Solution:
Step 1: Identify the key idea in the phrase: the victim is one's own child.Step 2: Recall that Foeticide refers to the killing of a fetus, usually before birth, which is different from killing a child already born.Step 3: Recognise that Filicide combines fili, meaning child or son, with cide, meaning killing, and therefore denotes killing of one's own child.Step 4: Understand that Infanticide refers to the killing of an infant, which may or may not be one's own child, so it is less precise for this definition.Step 5: Note that Lupicide describes killing of a wolf and is clearly unrelated to the given phrase.Step 6: Thus, Filicide is the one-word substitute that matches the phrase Killing of one's own child.

Verification / Alternative check:
Dictionaries and legal references define Filicide as the killing of one's own son or daughter. Infanticide is defined as the killing of an infant, often without reference to the relationship between the killer and the child. Foeticide is specifically associated with a fetus. Since the question stresses one's own child without limiting the age strictly to infancy or fetal stage, Filicide is the best and most accurate match. Infanticide, although close, does not include the idea of the killer being the parent, which is central to the phrase.

Why Other Options Are Wrong:
- Foeticide refers to the destruction of a fetus inside the womb and not to a child already born.
- Infanticide refers to killing an infant, which may be committed by anyone, not necessarily a parent, so it does not fully capture the idea of one's own child.
- Lupicide is killing of a wolf and clearly does not relate to human children.

Common Pitfalls:
Many learners confuse Filicide with Infanticide because both involve children. Examinations deliberately place these similar words together to test precise knowledge. Another pitfall is ignoring word roots and guessing randomly. A helpful technique is to learn common Latin roots: fili for child, infans for baby, foetus for unborn baby and lupus for wolf. Knowing these roots makes it easier to understand and remember the exact meanings of long words ending in cide.

Final Answer:
The correct one-word substitute for Killing of one's own child is Filicide.