He was surnamed Cursor from his swiftness of foot.
The speed with which it bounds upon its prey, when loosed from the cart, exceeds the swiftness of any other mammal.
The swiftness, the strength and the highly developed power of scent in the dog, have made it a powerful ally of man against the other animals; and perhaps these qualities in the dog were necessary to the establishment of society.
In spite of his small stature, he held his own amongst the other heroes before Troy; he was brave, next to Achilles in swiftness of foot and famous for throwing the spear.
The root is probably ak, with the idea of sharpness or swiftness (tiepos, wxus, acus, ocior).