Of uncertain origin. The word's original form was something like Proto-Italic *līðrā, *leiðrā (“pound”), surviving also in Ancient Greek λίτρα (lítra), whence English liter. Weiss derives the term from Proto-Indo-European *leyH- (“to pour”) suffixed with the instrumental/resultative suffix *-dʰrom, under the assumption that the term originally meant "pouring (of metal)" before evolving to mean a unit of weight. In this case, then cognate with Proto-Slavic *lìti (“to pour”), Proto-Celtic *liyeti (“to flow”), Ancient Greek λείβω (leíbō, “to pour”), Lithuanian li̇́eti (“to let flow”).