ˈsidˌnōn noun
( -s )
Etymology: Sydn ey, Australia (where this type of compound was discovered) + English -one
: any of a class of heterocyclic compounds that contain a ring composed of two carbon atoms, two nitrogen atoms, and a fifth atom (as oxygen) and have an oxo or similar group, that are resonance hybrids of several ionic states and have large dipole moments, and that are obtainable in various ways (as by dehydration of N -nitroso- N -phenyl-glycine by acetic anhydride)