osmious

from The Century Dictionary.

• Of or belonging to osmium; specifically, noting an oxid of osmium.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Chem.) Denoting those compounds of osmium in which the element has a valence relatively lower than in the osmic compounds.
• adjective (Chem.), an acid derived from osmium, analogous to sulphurous acid, and forming unstable salts. It is a brown amorphous substance.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective chemistry Denoting those compounds of osmium in which the element has a valence relatively lower than in the osmic compounds.