Is it farther or further?
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, from Vulgar Latin *christianus "a Christian," a generic term for "anyone," but often with a sense of "poor fellow." Related: Cretinism (1801).
cretin cre·tin (krēt'n)
A person afflicted with cretinism.