jejunumEnglishOxford New American Dictionaryjejunum /jəˈjo͞onəm, dʒəˈdʒunəm / ▸ noun (plural jejuna /-nə/) Anatomy the part of the small intestine between the duodenum and ileum. – DERIVATIVES jejunal /ˈjo͞onl/ adjective– ORIGIN mid 16th century : from medieval Latin, neuter of jejunus ‘fasting’ (because it is usually found to be empty after death).