cretin n.

1779, from French crétin (18c.), from Alpine dialect crestin, "a dwarfed and deformed idiot" of a type formerly found in families in the Alpine lands, a condition caused by a congenital deficiency of thyroid hormones. The word is of uncertain origin. By many it has been identified with Vulgar Latin *christianus "a Christian," a generic term for "anyone," but often with a sense of "poor fellow." Related: Cretinism (1796).