heroinhighly addictive narcotic derived from morphine: He had a hard time kicking heroin.Not to be confused with:heroine ? courageous woman; principle female character: The heroine of the play was a great actress.Abused, Confused, & Misused Words by Mary Embree Copyright © 2007, 2013 by Mary Embreeher·o·in (h?r??-?n)n. A white, odorless, bitter crystalline compound, C21H23NO5, that is derived from morphine and is a highly addictive illegal narcotic. Also called diacetylmorphine.[German, originally a trademark.]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.heroin (?h?r???n) n1. (Pharmacology) a white odourless bitter-tasting crystalline powder related to morphine: a highly addictive narcotic. Formula: C21H23NO5. Technical names: diamorphine or diacetylmorphine 2. (Recreational Drugs) a white odourless bitter-tasting crystalline powder related to morphine: a highly addictive narcotic. Formula: C21H23NO5. Technical names: diamorphine or diacetylmorphine [C19: coined in German as a trademark, probably from hero, referring to its aggrandizing effect on the personality]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014her?o?in (?h?r o? ?n) n. a white crystalline powder, C21H23NO5, derived from morphine, that is narcotic and addictive: manufacture or import is prohibited in the U.S. and other nations. [1895?1900; formerly trademark;