† hydrosulphurous,a.Chem.Obs.|-ˈsʌlfjʊrəs| [f. as prec. + sulphurous.] In hydrosulphurous acid, a name given first to dithionic acid; afterwards to hyposulphurous acid, or hydrogen hyposulphite, H2S2O4. 1855in Mayne Expos.Lex.1872–94[see hyposulphurous].