horehound
noun
hore·hound ˈhȯr-ˌhau̇nd 
1
a
: an Old World bitter perennial mint (Marrubium vulgare) with downy leaves
b
: an extract or confection made from the dried leaves and flowering tops of this plant
2
: any of several mints resembling the horehound
Example Sentences
Recent Examples on the Web Volunteers like Wright remove invasive plant species such as fennel, pampas grass, castor bean, fountain grass, horehound, Sahara mustard, tecolote. 
David Whiting, Orange County Register, 13 Jan. 2017
David Whiting, Orange County Register, 13 Jan. 2017 Word History
Etymology
Middle English horhoune, from Old English hārhūne, from hār hoary + hūne horehound — more at hoar
First Known Use
before the 12th century, in the meaning defined at sense 1a
Medical Definition
horehound
noun
hore·hound
variants also hoarhound
ˈhō(ə)r-ˌhau̇nd, ˈhȯ(ə)r-
1
: a European aromatic mint (Marrubium vulgare) that is naturalized in the United States, has pubescent leaves and small axillary flowers, has a very bitter taste, and is used as a tonic and anthelmintic
called also white horehound
2
: an extract or confection made from horehound and used as a remedy for coughs and colds