Final answer:
Etymologically, someone who commits perjury is C) A liar. Perjury means making false statements under oath and is derived from the Latin root 'perjurium'.
Step-by-step explanation:
Etymologically, someone who commits perjury is committing an act of lying while on oath in a court of law or any other legal proceeding. This is a serious offense as it involves deliberately making statements that one knows to be false, or not believing in the truth of the statements, while under oath. The correct answer to the question is C) A liar. Perjury comes from the Latin root 'perjurium', which means 'false oath'. In the context provided, those committing perjury are engaging in dishonesty to deceive others and sway legal processes.