Dibenzofuran
"Dibenzofuran, is a heterocyclic organic compound with the chemical 
structure shown at right. It is an aromatic compound that has two benzene rings fused to one furan ring in the middle. All of the numbered carbon atoms have a hydrogen atom bonded to each of them (not shown in the image). Dibenzofuran is an aromatic ether having the chemical formula C12H8O."
"Dibenzofurans can also inaccurately refer to polychlorinated dibenzofurans (PCDFs), a family of organic compounds with one or several of the hydrogens in the dibenzofuran structure replaced by chlorines. For example, 2,3,7,8-tetrachlorodibenzofuran (TCDF) has chlorine atoms substituted for each of the hydrogens on the number 2, 3, 7, and 8 carbons (see structure below). Polychlorinated dibenzofurans are much more toxic chemicals than the parent compounds with properties and chemical structures similar to polychlorinated dibenzodioxins. These groups together are often inaccurately called dioxins."