1. showing irritation or ill humor by a gloomy silence or reserve.
2. persistently and silently ill-humored; morose.
3. indicative of gloomy ill humor.
4. gloomy or dismal, as weather or a sound.
5. sluggish, as a stream.
6. Obsolete. malignant, as planets or influences.
"people can be sullen with people."
"people can be sullen with drapers."
"people can be sullen to bouts."
"people can be sullen for hours."
"people can be sullen beyond beliefs."
This list can help you learn new vocabulary more quickly and be able explore other words more easily.