The antonyms for the phrase "most unilluminated" include terms such as "brightest," "most illuminated," "brilliant," and "radiant." These words are used to describe objects, spaces or areas that are well-lit or have ample light sources. Additional antonyms for "unilluminated" are "bright," "luminous," "lighted," "gleaming," and "shining," which all denote an abundance of light. In contrast, "most unilluminated" can be used to convey a sense of darkness, shadow, or obscurity. These antonyms can be applied in various contexts, such as art, language, or literature, to depict different moods, emotions, or situations.