Osmious /(?)/

Os·mi·ous

Osmious

a.
  1. Denoting those compounds of osmium in which the element has a valence relatively lower than in the osmic compounds; as, osmious chloride. (Chem.)

Phrases & Compounds
Osmious acid
an acid derived from osmium, analogous to sulphurous acid, and forming unstable salts. It is a brown amorphous substance.