Duodenal is the doctor’s word for things that belong to the duodenum — the first, top stretch of the small bowel, sitting just under the stomach. Food leaves the stomach and goes into this short tube. When a doctor says a duodenal ulcer, they mean a sore in that stretch, not in the stomach itself (a stomach sore is a gastric ulcer). You almost never hear duodenal in the kitchen or the playground; it lives in hospitals, health news, and medical notes. It does not name the body part on its own: the part is the duodenum; duodenal tells you “of that part.”