horehound . ( Of the lat. )( marrubium ). 1. m. herbaceous plant of the family of the Labiadas, with stems erect, whitish, comose, home runs, four to six decimetres of height, leaves are oval, rough, with waves in the margin, hairy and more or less petiolate, white flowers in spikes, and nut with tiny seeds. It is very abundant in dry places plant and its flowers are used in medicine.