pyrimidines,
pyrimidine /pəˈrimədēn pīˈriməˌdēn/ I. noun 1. [Chemistry] a colorless crystalline compound with basic properties. [A heteroaromatic compound; chem. formula: C4H4N2.] 2. (also pyrimidine base) — [Chemistry] a substituted derivative of this, especially the bases thymine and cytosine present in DNA. – origin late 19th cent.: from German Pyrimidin, from pyridine, with the insertion of -im- from imide.
