Rhoticization of Old Latin ausum, from Proto-Italic *auzom, from Proto-Indo-European *h₂éws-o-m (or less likely *h₂é-h₂us-om) (“gold”), from *h₂ews- (“to dawn, become light, become red”). Cognate with Lithuanian áuksas, Old Lithuanian ausas, Old Prussian ausis, Tocharian A wäs, Tocharian B yasā.