a cap·pel·la (ä? k?-p?l??)adv. Music Without instrumental accompaniment.[Italian : a, in the manner of + cappella, chapel, choir.]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.a cappella or a capellaadj, adv (Classical Music) music without instrumental accompaniment[Italian: literally, according to (the style of the) chapel]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014a cap?pel?la (?? k??p?l ?) adv., adj. without instrumental accompaniment. [1875?80;