Mumpishly is a relatively uncommon word that means to be sullen or sulky. Its synonyms are words that also convey a negative and unenthusiastic attitude such as pouty, gloomy, moody, and sour. These words speak to the negative emotions that someone may be feeling when they are mumpish and their reluctance to engage with others. While these words have similar meanings, they may be used in specific contexts or situations. It is important to choose the right synonym to convey the correct tone and meaning, especially when trying to express emotions or to communicate effectively.