Armentières (ärməntērzˈ, Fr. ärmäNtyĕrˈ) [key], town (1990 pop. 26,220), Nord dept., N France, in Flanders, on the Lys River. It has foundries, boiler works, breweries, and a large textile industry. During most of World War I it was directly behind the Allied lines. It became known through the song "Mademoiselle from Armentières."