py·rim·i·dine (p?-r?m??-d?n?, p?-)n.1. A single-ringed, crystalline organic base, C4H4N2, that is the parent compound of a large group of biologically important compounds.2. Any of a group of substituted derivatives of pyrimidine, including the nitrogen bases uracil, cytosine, and thymine, which are components of nucleic acids. Barbiturates and certain other drugs are also pyrimidines.[Alteration of pyridine.]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.pyrimidine (pa??r?m??di?n) n1. (Elements & Compounds) a liquid or crystalline organic compound with a penetrating odour; 1,3-diazine. It is a weakly basic soluble heterocyclic compound and can be prepared from barbituric acid. Formula: C4H4N22. (Elements & Compounds) Also called: pyrimidine base any of a number of similar compounds having a basic structure that is derived from pyrimidine, including cytosine, thymine, and uracil, which are constituents of nucleic acids[C20: variant of pyridine]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014py?rim?i?dine (pa??r?m ??din, p?-) n. 1. a heterocyclic compound, C4H4N2, that is the basis of several important biochemical substances. 2. one of several pyrimidine derivatives, esp. the bases cytosine, thymine, and uracil, which are fundamental constituents of nucleic acids. [1880?85;b. pyridine and imide] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.py·rim·i·dine (p?-r?m??-d?n?) Any of a group of organic compounds having a single ring with alternating carbon and nitrogen atoms. Pyrimidines include the bases cytosine, thymine, and uracil, which are components of nucleic acids.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.