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(b) Prefixed to names of elements or radicals (or the combining forms, as bromo-, nitro-, oxy-, phospho-, azo-) entering into the name of a compound, to signify that four atoms or groups of the element or radical are substituted in the substance designated by the rest of the name, as tetrabromobenzene, C₆H₂Br₄, in which four of the hydrogen atoms of benzene, C₆H₆, are replaced by four bromine atoms; so tetramethylbenzene, C₆H₂(CH₃)₄.