From The Collaborative International Dictionary of English v.0.48:
Stannous \Stan"nous\ (-n[u^]s), a. (Chem.)
Pertaining to, or containing, tin; specifically, designating
those compounds in which the element has a lower valence as
contrasted with stannic compounds.
[1913 Webster]
Stannous chloride (Chem.), a white crystalline substance,
SnCl2.(H2O)2, obtained by dissolving tin in hydrochloric
acid. It is used as a mordant in dyeing.
[1913 Webster]