Merriam-Webster Collegiate Dictionary - vervain

 noun  Etymology: Middle English verveine, from Anglo-French, from Latin verbena leafy branch; akin to Latin verber rod, Lithuanian virbas, and perhaps to Greek rhabdos rod  Date: 14th century any of a genus (Verbena of the family Verbenaceae, the ~ family) of chiefly American plants having bracted spicate flowers, a corolla with a 5-lobed limb, and a fruit that separates into four nutlets