Dioxin

noun

1. Any of a broad range of toxic or carcinogenic halogenated polycyclic compounds that occur as byproducts of herbicides.
2. The parent compound, dibenzo-p-dioxin, in which two benzene rings are connected vio two oxygen atoms; oxanthrene.
3. The unsaturated six-membered heterocycle having four carbon atoms, two oxygen atoms and two double bonds.