Sullen/ˈsʌlən/ Definition 1 of 2Pro Tip 1/3Mood Indicator Use 'sullen' to describe someone showing irritation or ill humor by a gloomy silence. After losing the game, he had a sullen demeanor. Pro Tip 2/3Not Rude 'Sullen' suggests a silent moodiness, not rudeness or meanness. Her sullen attitude was more about her sadness than any dislike for us. Pro Tip 3/3Temporary State 'Sullen' often implies a temporary state rather than a permanent trait. He's usually cheerful, just a bit sullen today.