/ˌd(y)o͞oəˈdēnəm/ /d(y)o͞oˈädn-əm/
Noun, pl. duodena or duodenums
1. The first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine may be used instead of duodenum. (wikipedia.org)
2. The part of the small intestine between the stomach and the jejunum. (wordnetweb.princeton.edu)
3. The first or proximal portion of the small intestine, extending from the pylorus to the jejunum, so called because it is about 12 fingerbreadths in length. (biology-online.org)
Word origin: From Latin duodenum, from duodeni ‘twelve each’, from duodecim ‘twelve (from duo ‘two’ + decem ‘ten’)