From Proto-Celtic *awontro (compare Cornish ewnter), oblique of *awontīr (compare Welsh ewythr), from pre-Celtic *h₂eu-on-tēr, from Proto-Indo-European *h₂ewh₂- (“relative, descendant”), *h₂éwh₂os (compare Middle Irish ó, Latin avus (“grandfather”), dialectal German Awwe).