Ferrous
In chemistry, the adjective ferrous indicates a compound that contains iron in the +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to "ferric", which indicates presence of iron in a +3 oxidation state, such as the trivalent cation Fe3+. This usage has been largely replaced by the IUPAC nomenclature, which calls for the oxidation state being indicated by Roman numerals in parentheses, such as iron oxide for ferrous oxide, iron oxide for ferric oxide, and iron oxide for the oxide that contains both forms of iron.
of aqueous iron
Outside chemistry, "ferrous" means generally "containing iron". The word is derived from the Latin word ferrum. Ferrous metals include steel and pig iron and alloys of iron with other metals. "Non-ferrous" is used to describe metals and alloys that do not contain an appreciable amount of iron.
The term "ferrous" is usually applied only to metals and alloys. The adjective is used instead to refer to non-metallic substances that contain iron, such as "ferruginous water"; or to an orangish-brown color resembling that of rust.
