Water horehound : Bugleweed.

Example:


Taxonomy
herb, horehound, plant, Herbal History, remedy, leaves, Black Horehound, Garden Herbs, juice, sides, honey, white horehound, Marrubium, square, labiate, waste places, botanical, volatile oil.

Defination from the web:
Horehound tea may be made by pouring boiling water on the fresh leaves, an ounce to a pint, and sweetening this with honey: then a wineglassful ... The Water Horehound (Lycopus), or gipsy wort, which grows frequently in our damp meadows and on the sides of streams, yields a black dye used for ...