opisthion

The story

1. Ancient Greek · derived fromὀπίσθιος“rear, behind”
2. New Latin · borrowed fromopisthion
3. English todayopisthion

From New Latin opisthion, from Ancient Greek ὀπίσθιος (opísthios, “rear, behind”), from ὄπισθεν (ópisthen, “at the back, backwards”). By surface analysis, opisth- + -ion.