- A double-ringed, crystalline organic base, C5H4N4, not known to occur naturally, from which is derived the nitrogen bases adenine and guanine, as well as uric acid as a metabolic end product. (noun)
- Any of a group of organic compounds structurally related to purine, particularly adenine and guanine, and also caffeine, uric acid, theobromine, and theophylline. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.