Definition of the dead nettle are a plants of the genus Pilea having drooping green flower clusters and smooth translucent stems and leaves any of various plants of the genus Lamium having clusters of small usually purplish flowers with two lips foul-smelling perennial Eurasiatic herb with a green creeping rhizome coarse bristly Eurasian plant with white or reddish flowers and foliage resembling that of a nettle; common as a weed in United States .