early 13c., from Old Norse kaka "cake," from West Germanic *kokon- (cf. Middle Dutch koke, Dutch koek, Old High German huohho, German Kuchen). Not now believed to be related to Latin coquere "to cook," as formerly supposed. Replaced its Old English cognate, coecel.
Originally (until early 15c.) "a flat, round loaf of bread." Piece of cake "something easy" is from 1936. The let them eat cake story is found in Rousseau's "Confessions," in reference to an incident c.1740, long before Marie Antoinette, though it has been associated with her since c.1870; it apparently was a chestnut in the French royal family that had been told of other princesses and queens before her.