Which word describes something that is only slightly relevant or goes off-topic?

The word "tangential" describes something that is only slightly relevant or deviates from the main topic. When a discussion or argument veers off into tangential points, it indicates that those points are not at the heart of the issue and may not significantly contribute to the main conversation. This term is often used in academic or formal contexts where the focus is important, and anything tangential may serve as a distraction or a less relevant detail.

In contrast, "substantial" refers to something of considerable importance, size, or value, which is quite the opposite of indicating slight relevance. "Essential" implies that something is absolutely necessary or fundamental, again highlighting importance rather than a lack thereof. Lastly, "peripheral" can also relate to something being on the periphery or outer edge, which can suggest a lack of direct importance but doesn't explicitly convey the sense of deviation from the main topic as clearly as "tangential" does. Thus, "tangential" is the most accurate choice for describing something that is only slightly relevant or off-topic.