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. {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.