E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Mental imbecility accompanied by goître. So called from the Crétins of the Alps. The word is a corruption of Christian (Chrétien), because, being baptised, and only idiots, they were washed from original sin, and incapable of actual sin. Similarly, idiots are called innocents. (French crétin, crétinisme.)