Which term describes the opposing side of an argument?

The term that describes the opposing side of an argument is "counterargument." A counterargument presents a viewpoint that challenges or contradicts the main argument being made. It serves to acknowledge and address opposing perspectives, which is an essential part of forming a well-rounded argument. By including a counterargument, a writer or speaker demonstrates an understanding of the complexity of the issue and strengthens their position by effectively responding to potential objections.

The other terms relate to the structure of argumentation but do not represent the opposing side. A claim refers to the main point or assertion being argued. Support and evidence pertain to the information or reasoning used to back up a claim but do not directly address opposing viewpoints. Therefore, "counterargument" is the most accurate descriptor for the opposing side of an argument.