also goddamn, late 14c., "the characteristic national oath of Englishmen" [Century Dictionary]. from God + damn (v.). Goddam (Old French godon, 14c.) was said to have been a term of reproach applied to the English by the French.
Mais, fussent-ils [les anglais] cent mille Goddem de plus qu'a present, ils n'auront pas ce royaume. [Joan of Arc, 1431, quoted in Prosper de Barante's "Histoire des ducs de Bourgogne"]
Hence French godan "fraud, deception, humbug" (17c.). Compare Old French godeherre "characteristic exclamation uttered by the Germans," and goditoet, also considered a characteristic exclamation of the English. Goddammes was the nickname given by Puritans to Cavaliers, in consequence of the latter's supposed frequent employment of that oath.