but·ton·bush (b?t?n-bo?osh?)n. A deciduous North American shrub (Cephalanthus occidentalis) having opposite leaves and spherical clusters of small white flowers.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.buttonbush (?b?t?nb??) na N American shrub of the genus CephalanthusCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014but?ton?bush (?b?t n?b??) n. a North American shrub, Cephalanthus occidentalis with globular flower heads. [1625?35] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.