I. ˌsa-krō-ˈi-lē-ˌak, ˌsā- adjective
Etymology: probably from French sacro-iliaque, from New Latin sacrum + French iliaque iliac
Date: 1831
: of, relating to, or being the region of juncture of the sacrum and ilium
II. noun
Date: 1936
: the sacroiliac region ; also : its firm fibrous cartilage