lily of the valleyn. pl. lilies of the valley A widely cultivated ornamental plant (Convallaria majalis) having one-sided racemes of fragrant, bell-shaped 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.lily of the valley n, pl lilies of the valley (Plants) a small liliaceous plant, Convallaria majalis, of Eurasia and North America cultivated as a garden plant, having two long oval leaves and spikes of white bell-shaped flowersCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014lil?y of the val?ley n., pl. lilies of the valley. a plant, Convallaria majalis, of the lily family, having an elongated cluster of small, drooping, bell-shaped, fragrant white flowers. [1555?65] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.