"Hydrosulphurous" is a word in ENGLISH

A prefix denoting that the element to the name of which it is prefixed enters with a low valence, or …

A salt of hyposulphuric acid.

A salt of hyposulphurous acid proper.

A salt of what was formerly called hyposulphurous acid; a thiosulphate.

Pertaining to, or containing, sulphur in a lower state of oxidation than in the sulphuric compounds; as, hyposulphuric acid.

Of, pertaining to, or designating, any one of a series of acids regarded as acid ethereal salts of hyposulphurous acid; …

Of, pertaining to, or designating, an unstable acid, H2S2O3, analogous to sulphuric acid, and formerly called hyposulphurous acid.