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Webster 1913 Edition
Osmious
Os′mi-ous
,Adj.
 (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.