Where does “αίγαγρος” come from?

αίγαγρος (Greek) comes from Ancient Greek αἴγαγρος, from Latin pila, from Latin pīlus, from Latin pīlum, from Proto-Italic pistlom, from Proto-Indo-European pis-tlo-, from Proto-Indo-European peys- — to grind, to crush.

αίγαγρος (Greek): ibex, chamois, wild goat