ribosomal RNAn. Abbr. rRNA The RNA that is a permanent structural part of a ribosome.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.ribosomal RNA n (Biochemistry) biochem a type of RNA thought to be transcribed from DNA in the nucleoli of cell nuclei, subsequently forming the component of ribosomes on which the translation of messenger RNA into protein chains is accomplished. Sometimes shortened to: rRNA Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ribosomal RNA n. a type of RNA, distinguished by its length and abundance, that functions in protein synthesis as a component of ribosomes. Abbr.: rRNA [1960?65] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.