The Collaborative International Dictionary
osmous
Osmious \Os"mi*ous\, a. (Chem.) Denoting those compounds of osmium in which the element has a valence relatively lower than in the osmic compounds; as, osmious chloride. [Written also osmous.]
Osmious acid (Chem.), an acid derived from osmium, analogous to sulphurous acid, and forming unstable salts. It is a brown amorphous substance.