The word "most atrabilious" is a term used to describe someone who is exceptionally irritable, melancholic, or gloomy. Antonyms for this term would be words that describe the opposite of these qualities, such as cheerful, optimistic, or upbeat. Some other antonyms for "most atrabilious" could include contented, satisfied, or hopeful. These are all words that describe a positive and happy disposition, which is the opposite of the negative and gloomy attitude implied by "most atrabilious". By using antonyms like these, we can better understand the range of emotions and attitudes that exist within our everyday experiences.