When someone is feeling sullen, they're being uncommunicative and moody. They may also be sulking, brooding, or acting distant. Other synonyms for sullenness include melancholy, glumness, moroseness, and despondency. These emotions can be triggered by a variety of factors, such as a bad day, a fight with a loved one, or just general dissatisfaction with life. Regardless of the cause, it's important to recognize when someone is feeling sullen and try to offer comfort or support. Sometimes, all it takes is a listening ear or a small act of kindness to turn someone's day around and lift their mood.