horse-radish, perennial herb ( Armoracia rusticana, but sometimes classified in other genera) of the family Cruciferae (mustard family), native to central and S Europe (where it has long been cultivated in gardens) and naturalized in many parts of North America. It is grown mainly for its roots, which formerly were used medicinally, particularly as an antiscorbutic. Today the roots make a popular condiment and are usually grated and mixed with vinegar to make a sauce or relish for meats and sea food. The lively pungency of the root is caused by its volatile oil, which resembles mustard oil. The wilted foliage has been used as a poultice to relieve toothache and facial neuralgia. An old name for it is German mustard. Horse-radishes are classified in the division Magnoliophyta, class Magnoliopsida, order Capparales, family Cruciferae.