illium

"Illium" is a term encountered chiefly as a variant spelling or misspelling of several distinct words and names. Depending on context, it may refer to anatomical structures, historical toponyms, or fictional places.

In anatomy, the correct term is ilium (single "l"), the largest and uppermost part of the hip bone (os coxae). The ilium forms the iliac crest, contributes to the acetabulum that articulates with the femur, and joins the sacrum at the sacroiliac joint. The spelling "illium" is a common typographical error in medical and educational materials.

In historical and literary contexts, Ilium (also spelled Ilion) is the classical Latin and Greek name for the ancient city commonly known as Troy. Some modern texts or informal usages render this as "Illium," but the traditional scholarly form uses a single "l."

In popular culture, Illium (double "l") appears as a proper name in fictional settings, most notably as a fictional planet or city in science fiction works and video games. In such uses, the spelling is intentional and denotes a distinct place within a created universe rather than the anatomical or ancient-city senses.

Because of these different uses, readers encountering "Illium" should consider context to determine whether it is an orthographic variant, an intentional fictional name, or a reference requiring the standard forms "ilium" or "Ilium."