Which word signifies a powerfully persuasive argument?

The word that signifies a powerfully persuasive argument is "cogent." A cogent argument is clear, logical, and convincing, effectively persuading the audience due to its sound reasoning and well-structured presentation. This term is often used in contexts where the strength and clarity of reasoning are crucial for persuasion, such as in debates, essays, or legal arguments.

In contrast, "discourse" refers to written or spoken communication and does not inherently imply persuasion. "Discretion" involves the quality of having or displaying good judgment, particularly in speech or conduct, but is unrelated to the nature of an argument itself. "Candor" denotes openness and honesty, especially in expression, but it also does not specifically relate to the persuasive nature of an argument. Thus, "cogent" stands out as the term that directly relates to the idea of a strong and persuasive argument.