Ilium \Il"i*um\, n. [See Ileum.]

(Anat.) The dorsal one of the three principal bones comprising either lateral half of the pelvis; the dorsal or upper part of the hip bone. See Innominate bone, under Innominate. [Written also ilion, and ileum.]

Source: Webster's Revised Unabridged Dictionary (1913)
 

Ileum \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.

Source: Webster's Revised Unabridged Dictionary (1913)