Where does “άσφαλτος” come from?

άσφαλτος (Greek) comes from Ancient Greek ἄσφαλτος, from Ancient Greek ἀ-, from Proto-Hellenic hə-, from Proto-Indo-European sm̥-, from Proto-Indo-European sem- — together, one.

άσφαλτος (Greek): free from errors; asphalt, asphalt road