inclusion bodyn. An abnormal structure in a cell nucleus or cytoplasm having characteristic staining properties and usually composed of protein, occurring primarily in infectious diseases, especially viral infections such as rabies.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.inclusion body n (Pathology) pathol any of the small particles found in the nucleus and cytoplasm of cells infected with certain viruses Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014