Proto-Indo-European *h₁el- (“swan”). Cognates within Celtic include Breton alarc’h, Cornish alargh, Welsh alarch, and outside Celtic Latin olor and Ancient
moged ar pakad a zo aet endeo. (Mich Beyer, Seizh Devezh Warn-ugent, An Alarc'h Embannadurioù, 2006, p. 15.) Mentioned in the Dictionnaire François-Celtique