horseradish - a cruciferous plant (Cochlearia Armoracia), with white flowers and broad rough leaves, a native of middle Europe and western Asia, commonly cultivated for its root, horseradish - hardy perennial plant of the mustard family (Brassicaceae, or Cruciferae) or its hotly pungent, fleshy root, used as a condiment or table relish mainly in the form of a sauce to enhance