Sullen and Gloomy are both adjectives used to describe a person's mood or attitude. Sullen is defined as having a bad temper, being sullenly silent, and having a gloomy outlook. Gloomy, on the other hand, is defined as having a dark, dismal, and depressing atmosphere. Both terms can be used to describe someone who is feeling down or depressed. The term 'GLUM' is also often used to describe someone who is feeling this way, and it is a four-letter word that is similar in meaning to both Sullen and Gloomy.