Which word indicates a sense of uncertainty or doubt in a statement?

The choice "ambiguous" is correct because it specifically describes a lack of clarity and precision that often leads to uncertainty or doubt in a statement. When something is ambiguous, it can be interpreted in multiple ways, which creates confusion about its meaning and intention. This inherent vagueness fosters an environment where certainty is lost, making it difficult for the listener or reader to grasp the speaker's or writer's true intent. Thus, "ambiguous" effectively conveys the idea of doubt.

In contrast, the other options reflect clarity and certainty. An affirmative statement is one that clearly asserts a position or agreement. A definite expression leaves little room for interpretation, providing a clear and specific understanding. Similarly, something that is conclusive offers a final determination, eliminating any doubt. Therefore, "ambiguous" stands out as the only option that embodies uncertainty or doubt in a statement.