*arþrą

From Proto-Indo-European *h₂érh₃-tro-m, a neuter instrument noun from *h₂erh₃- + *-tro-m; (Kroonen 2017: 105–10; Kroonen et al. 2022: 45; Weiss 2020: 484–85; Wodtko et al. 2008: 323). The *-tro- variant is expected after a root containing a liquid (Olsen 1988: 12, 16). Cognate with Ancient Greek ἄροτρον (árotron), Old Armenian արաւր (arawr), Old Irish arathar, and Welsh aradr; Latin arātrum was remodeled after the verbal present stem (de Vaan 2008: s.v. arō, -āre).