birth·root (bûrth?ro?ot?, -ro?ot?)n. See trillium.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.birthroot (?b????ru?t) n (Plants) any of several North American plants of the genus Trillium, esp T. erectum, whose tuber-like roots were formerly used by the Native Americans as an aid in childbirth: family TrilliaceaeCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014birth?root (?b?r??rut, -?r?t) n. 1. a trillium, Trillium erectum, the roots of which were formerly used in medicine as an astringent. 2. any of certain other trilliums. [1815?25] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.