tone·less (t?n?l?s)adj.1. Lacking tone.2. Lacking vitality; listless.tone?less·ly adv.tone?less·ness n.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.toneless (?t??nl?s) adj1. having no tone2. lacking colour or vitality ?tonelessly adv ?tonelessness nCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014