pyr·i·done \ˈpirəˌdōn\noun (-s) Etymology: International Scientific Vocabulary pyrid- + -one : any of several isomeric carbonyl compounds C5H5NO derived from pyridine: as a.: the crystalline alpha isomer — called also 2-pyridone, 2(1H)-pyridone b.: the crystalline gamma isomer — called also 4-pyridone, 4(1H)-pyridone