Gliadin: A glycoprotein (a carbohydrate plus a protein) within gluten. Gliadin is found in wheat and some other grains, including oats, rye, barley, and millet. People with celiac disease, Crohn's disease, and other conditions may be sensitive to gliadin in the diet. In these conditions, antibodies to gliadin can often be detected in the blood. See also: Gluten enteropathy.