Is'chi·al (ĭs'kĭ* a l) adjective (Anat.) Of or pertaining to the ischium or hip; ischiac; ischiadic; ischiatic. Ischial callosity (Zoology) , one of the patches of thickened, hairless, and often bright-colored skin, on the buttocks of many apes, as the dri... Found on http://www.encyclo.co.uk/webster/I/100