Most rayless means having the least amount of light or brightness. So, some antonyms for most rayless could be bright, radiant, luminous, glowing, dazzling, brilliant, shining, vivid, radiant, and flamboyant. These words describe various intensities of light and color that are the opposite of most rayless. On the other hand, some synonyms for most rayless include dark, dim, gloomy, somber, dusky, murky, and bleak. Using antonyms and synonyms can help a writer to describe the scene with greater detail and precision, to convey different moods, and to engage the reader's senses.