Webster’s Revised Unabridged Dictionary · 1913
Ischial
Is′chi·al (ĭs′kĭ·al), a. (Anat.) Of or pertaining to the ischium or hip; ischiac; ischiadic; ischiatic.
Ischial callosity (Zoöl.), one of the patches of thickened, hairless, and often bright-colored skin, on the buttocks of many apes, as the drill.