It is called the cowage, or cow-itch, on account of the seed pods being covered with short brittle hairs, the points of which are finely serrated, causing an unbearable itching when applied to the skin, which is relieved by rubbing the part with oil.    From Wordnik.com.  [Catalogue of Economic Plants in the Collection of the U. S. Department of Agriculture] Reference

Nettle of extra-stinging quality; but it may also mean an Eastern plant that was used to produce cowage, or cow-itch.    From Wordnik.com.  [The plant-lore & garden-craft of Shakespeare] Reference