- au French, "at the, to the," from O.Fr. al, contraction of a le, with -l- softened to -u-, as also poudre from pulverem, chaud from calidus, etc. Used in many expressions in cookery, etc., which have crossed the Channel since 18c., e.g. au contraire, lit. "on the contrary;" au gratin, lit. "with scrapings;" au jus, lit. "with the juice."
Etymology dictionary. 2014.