Any of several plants of the genus Eupatorium in the composite family, especially the eastern North American species E. perfoliatum, having opposite leaves united around the stem and clusters of small white flower heads. Also called thoroughwort.
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.