Etymology

From Middle Irish aithrigid ‎(“to change, alter, move”), from Old Irish ad·eirrig ‎(“to repeat, reiterate; change”), from ath- + ar- + Proto-Celtic *rego- (whence also Old Irish at·reig, Scottish Gaelic èirich), from Proto-Indo-European *h₃reǵ- ‎(“to straighten”). Cognate with Irish athraigh.