\Il"e*um\, n. [L. ile, ileum, ilium, pl. ilia, groin,
flank.]
1. (Anat.) The last, and usually the longest, division of the
   small intestine; the part between the jejunum and large
   intestine. [Written also {ileon}, and {ilium}.]
2. (Anat.) See {Ilium}. [R.]
Note: Most modern writers restrict ileum to the division of
      the intestine and ilium to the pelvic bone.