thiosulphatePronunciation: /ˌθʌɪə(ʊ)ˈsʌlfeɪt/ (US thiosulfate)Definition of thiosulphate noun Chemistry a salt containing the anion S2O32−, i.e. a sulphate with one oxygen atom replaced by sulphur. thiosulphate in other Oxford dictionaries Definition of thiosulphate in the US English dictionary