- Either of two isomeric unsaturated cyclic compounds having the formula C<sub>6</sub>H<sub>4</sub>O<sub>2</sub>, found widely in plants, especially in a yellow crystalline form, and used in making dyes, tanning hides, and photography.
- Any of various quinonoid compounds, often yellow to red in color, many of which have biological derivation or importance, such as coenzyme-Q.
- The general name applied to all benzene derivatives in which two hydrogen atoms are replaced by two oxygen atoms.
- Specifically, a compound obtained by distilling kinic acid with diluted sulphuric acid and peroxid of manganese, or by the oxidation of aniline with chromic acid.
- A crystalline substance, C6H4O2 (called also <altname>benzoketone</altname>), first obtained by the oxidation of quinic acid and regarded as a double ketone; also, by extension, any one of the series of which quinone proper is the type.
- any of a class of <xref>aromatic</xref> compounds having two <xref>carbonyl</xref> <xref>functional groups</xref> in the same six-membered <xref>ring</xref>
- any of a class of aromatic yellow compounds including several that are biologically important as coenzymes or acceptors or vitamins; used in making dyes