Ilium

Definition
noun, plural: ilia
The uppermost and the largest bone of the pelvis that is composed of two major parts in humans: the body and the ala. This bone articulates on the inner aspect with the sacrum.
Supplement
The iliac bone or the ilium is found in most vertebrates such as mammals, reptiles (but not all snakes) and birds. It is not found in bony fish.
(Note: ilium should not be confused with the term ileum, which pertains to a section of the small intestine)
Word origin: from the Latin, meaning “groin” or “flank.”
Also called: iliac bone
See also: pelvis, biiliac width