Noctilucent is a word that describes something that emits light at night. Its antonyms would be words that describe the opposite, something that does not emit light at night. Some possible antonyms could include dark, black, unlit, dim, shadowy, and gloomy. These words suggest the absence of light, either natural or artificial, and could be used to describe places or objects that are often associated with darkness, such as caves, dungeons, or basements. While noctilucent has a positive connotation, suggesting something mysterious or magical, its antonyms evoke more negative emotions, such as fear, sadness, or loneliness.