in·tra·mus·cu·lar (?n?tr?-m?s?ky?-l?r)adj. Within a muscle: an intramuscular injection.in?tra·mus?cu·lar·ly adv.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.intramuscular (??ntr??m?skj?l?) adj (Anatomy) anatomy within a muscle: an intramuscular injection. Abbreviation (esp of an injection): IM or i.m. ?intra?muscularly advCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014in?tra?mus?cu?lar (??n tr??m?s ky? l?r) adj. located or occurring within a muscle. [1870?75] in`tra?mus?cu?lar?ly, adv. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.