dioxin

1. A ring consisting of two oxygen atoms, four CH groups, and two double bonds; the positions of the oxygen atoms are specified by prefixes, as in 1,4-dioxin.
2. Abbreviation for dibenzo[b,e][1,4]dioxin which may be visualized as an anhydride of two molecules of 1,2-benzenediol (pyrocatechol), thus forming two oxygen bridges between two benzene moieties, or as a 1,4-dioxin with a benzene ring fused to catch each of the two CH=CH groups.
3. A contaminant in the herbicide, 2,4,5-T; it is potentially toxic, teratogenic, and carcinogenic.