The word "acherontic" is not common in everyday language, and its meaning refers to something dark or gloomy related to the River Acheron in Greek mythology, which was believed to lead to the underworld. Therefore, finding antonyms for "more acherontic" can be a challenging task. However, some alternatives that could convey the opposite of darkness and gloom include bright, cheerful, sunny, joyful, luminous, and lively. These words could suggest lightness, happiness, and positivity, which are the complete opposite of the concept of "more acherontic." Ultimately, choosing an adequate antonym for this rare term will depend on the context and feeling that the speaker or writer wants to convey.