Counterplan is a term that commonly used in debates when one side presents an alternative plan to the one proposed by the other. In such cases, the word "counter" hinted at a plan that would oppose the prior plan. A few synonyms for counterplan can offer variety in discussions or disputes, which is crucial to put forward new ideas or approaches. Some of the alternative terms of counterplan include alternative plan, rival plan, opposing plan, and competing plan. To put it differently, you could use "opposing strategy" or "clashing proposal" to express the notion of a counterplan in a unique way that suits the context.