The antonyms for "upper-most" are "lowermost," "bottommost," "lowest," and "undermost." These words suggest the lowest ranking or position of something relative to everything else. Compared to the "uppermost" level, which refers to the highest or top-most position in a hierarchy, the "lowermost" or "bottommost" position insinuates inferiority or subservience. The words "lowest" and "undermost" simply indicate positioning at the very bottom. The antonyms of "upper-most" are important because they describe a completely different context and perspective, whether in terms of geography, social status or organizational structure. They complete our understanding of a thing, helping us compare its position, value or importance to other things in a hierarchy.