Is it ensure, insure, or assure?
"pertaining to the hip," also in reference to the large nerve from the pelvis to the thigh, 1540s, from Middle French sciatique (14c.), from Medieval Latin sciaticus (see sciatica).
sciatic sci·at·ic (sī-āt'ĭk)adj.
Of or relating to the ischium or to the region of the hipbone in which it is located.
Of or relating to sciatica.