Entry 1 sense Webster, 1913 Thiosulphate · Thi·o·sul·phate · IPA /θaɪə(ʊ)ˈsʌlfeɪt/ 01 n. A salt of thiosulphuric acid; -- formerly called hyposulphite. 1. A salt of thiosulphuric acid; -- formerly called hyposulphite.(Chem.) Also: hyposulphite