The Collaborative International Dictionary
Platinous
Platinous \Plat"i*nous\, a. (Chem.) Of, pertaining to, or containing, platinum; -- used specifically to designate those compounds in which the element has a lower valence, as contrasted with the platinic compounds; as, platinous chloride ( PtCl2).
Wiktionary
platinous
a. (context inorganic chemistry English) Containing divalent platinum.