ileum vs small intestine

ileum and small intestine both are nouns.

Word	Noun	Adjective	Verb	Adverb
ileum	Yes	No	No	No
small intestine	Yes	No	No	No

As nouns, small intestine is a hypernym of ileum; that is, small intestine is a word with a broader meaning than ileum:

ileum: the part of the small intestine between the jejunum and the cecum
small intestine: the longest part of the alimentary canal; where digestion is completed

ileum (noun)	small intestine (noun)
the part of the small intestine between the jejunum and the cecum	the longest part of the alimentary canal; where digestion is completed