rag·wort (r?g?wûrt?, -wôrt?)n. Any of various plants in the composite family, chiefly of the genera Senecio and Packera, having yellow flower heads. S. jacobaea, a European species poisonous to livestock, is widely naturalized in North America and elsewhere.[From the ragged shape of its leaves.]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.ragwort (?ræ??w??t) n (Plants) any of several plants of the genus Senecio, esp S. jacobaea of Europe, that have yellow daisy-like flowers: family Asteraceae (composites). See also groundsel1Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014rag?wort (?ræg?w?rt, -?w?rt) n. any of various composite plants of the genus Senecio, usu. bearing yellow, slender-rayed flower heads. [1325?75] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.