tone clustern. A dissonant group of closely spaced notes played at the same time.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.tone cluster n (Classical Music) music a group of adjacent notes played simultaneously, either in an orchestral score or, on the piano, by depressing a whole set of adjacent keys Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014