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.]

[1913 Webster]

Osmious acid (Chem.), an acid derived from osmium, analogous to sulphurous acid, and forming unstable salts. It is a brown amorphous substance. [1913 Webster]

Source: The Collaborative International Dictionary of English v.0.48
 

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.

Source: Webster's Revised Unabridged Dictionary (1913)