Merriam-Webster Collegiate Dictionary - comfrey

 noun  (plural ~s)  Etymology: Middle English cumfirie, from Anglo-French cunfirie, from Latin conferva a water plant, from confervere to grow together (of bones), from com- + fervere to boil — more at barm  Date: 13th century  1. any of a genus (Symphytum) of perennial herbs of the borage family with coarse hairy entire leaves and flowers in one-sided racemes  2. an herbal preparation of the leaves or roots of ~ that is toxic if taken internally