What is the term for evidence that undermines an opponent’s position?

The term that specifically refers to evidence that undermines an opponent’s position is "rebuttal." A rebuttal typically involves presenting arguments or facts that contradict the claims made by the opposing party, effectively discrediting or challenging their position. It serves as a critical element in debate and logical discourse, where each side aims to prove its point while countering the claims of the opposition.

The nature of a rebuttal is to directly address and refute the arguments presented by an opponent, thereby strengthening one's own position in the discussion. This makes it a key component in any argumentative exchange, whether in written form or oral debates.

The other choices, while related to argumentative discourse, do not capture this specific action of undermining an opponent’s stance. A counterargument, for instance, presents an alternative viewpoint but doesn’t necessarily focus solely on discrediting the opponent. An assertion is a confident statement of belief or fact without requiring evidence, and a premise serves as a foundational statement upon which an argument is built, rather than as a tool for undermining another's position.