dithionitePronunciation: /dʌɪˈθʌɪənʌɪt/Definition of dithionite noun Chemistry a salt containing the anion S2O42−. Origin: mid 20th century: from di-1 'two' + Greek theion 'sulphur' + -ite1dithionite in other Oxford dictionaries Definition of dithionite in the US English dictionary