1.NounA substituted benzimidazole (trademark Losec, Prilosec) which is a proton pump inhibitor and inhibits secretion of gastric acid, being given orally in the treatment of ulcers and gastroesophageal reflux; 5-methoxy-2-(4-methoxy-3,5-dimethyl-2-pyridylmethylsulfinyl)benzimidazole, C17H19N3O3S.