N-ni·tro·so·di·meth·yl·a·mine (?n?n?-tr??s?-d?-m?th??-l?-m?n?, -?-l?m??n, -n??tr?-, )n. See NDMA.[N-, prefix indicating that a functional group has been substituted for a hydrogen atom on the nitrogen atom in an amide + nitrosodimethylamine.]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.