white horehound: A genus of the gymnophyllum order, belonging to the didynamia class of plants; and in the natural method ranking under the 42d order, Verticillata. The calyx is salver-shaped, rigid, and ten-fractured; the upper lip of the corolla bifid, linear, and straight. There are nine species, the most remarkable of which is the vulgare, a native of Britain, growing naturally in waste places, and by way-side near towns and villages, but not common. It has a strong and somewhat musky smell, and bitter taste. It is reputed attenuant and resolvent; an infusion of the leaves in water, sweetened with honey, is recommended in asthmatical and phthisical complaints, and most other diseases of the breast and lungs.