Emily Dickinson Lexicon

CAS'TOR-OIL, n. [A corruption of Castus oil, the plant producing it having formerly been called Agnus castus.]

The oil of the Ricinus communis, or Palma Christi, a plant of the West Indies, which grows to the highth of twenty feet in one season. The oil is obtained from the nuts or seeds by expression or decoction. That obtained by decoction is preferred, as less liable to become rancid, being free from the mucilage and acrid matter, which is mixed with the oil when expressed. It is a mild cathartic. – Encyc.