1841 in cookery, reborrowing from French of the same word that had been taken 14c. and Englished as fillet (q.v.). Filet mignon (literally "dainty fillet") for "small, round, tender cut of meat from the center of the fillet" is attested as a French word in English from 1815.
The 'Chateaubriand,' the 'entrecôte,' and the 'filet mignon' (of mutton), with other forms, are all due to the more enlarged sympathies of the French butcher for what is perfect. We must entirely change the mode of cutting up the carcase before we can arrive at the same perfection in form of meat purchasable, and as that is hopeless, so is it useless to insist further on the subject on behalf of the public. ["The Kitchen and the Cellar," Quarterly Review, April 1877]
c. 1500, "a favorite; a darling, one who or that which is beloved" (a sense now obsolete), from Old French mignon "a favorite, darling" (n.), also a term of (probably homosexual) abuse; as an adjective, "dainty, pleasing, favorite," from mignot "pretty, attractive, dainty, gracious, affectionate." The French word is of uncertain origin, perhaps from Celtic (compare Old Irish min "tender, soft"), or from Old High German minnja, minna "love, memory" (see minnesinger).
Used 16c.-17c. without disparaging overtones, but also from c. 1500 as "a favorite of a sovereign prince," especially "an intriguing favorite, a low or servile dependent." It also was used from 16c. for "a pert or saucy girl."