The Collaborative International Dictionary
Selenious
Selenious \Se*le"ni*ous\, a. [Cf. F. s['e]l['e]nieux.] (Chem.) Of, pertaining to, or containing, selenium; specifically, designating those compounds in which the element has a lower valence as contrasted with selenic compounds.
Wiktionary
selenious
a. (context inorganic chemistry English) Of, pertaining to, or containing selenium, especially in a lower oxidation state than corresponding selenic compounds