Which word signifies something that is not relevant to the topic at hand?

The word "extraneous" effectively signifies something that is not relevant to the topic at hand because it specifically refers to information or elements that are unrelated or unnecessary in a particular context. When discussing a subject or issue, extraneous details can detract from the main focus, leading to confusion or distraction.

In contrast, the other terms carry meanings that are more aligned with relevance or importance. "Pertinent" describes something that is directly related and applicable to the matter being discussed, making it essential for understanding the topic. "Essential" refers to something that is absolutely necessary or fundamental, reinforcing the idea of importance. Similarly, "significant" indicates something that has meaning or importance in a particular situation, which again contrasts with the notion of irrelevance found in "extraneous."