Peter's-wort: A genus of the polyandra order, belonging to the polydelphin class of plants; and in the natural method ranking under the 20th order, Rotaceæ. The calyx consists of four leaves; the corolla has four petals; the filaments are numerous, and divided into four bundles. There are three species, the crux andreea, the hypericoides, and the villosum, all natives of the West Indies or America, but possessing no property worthy of notice.