What does ferrous mean?
Ferrous is an adjective describing something that contains or relates to iron. In everyday and industrial language it most often appears in the phrase 'ferrous metals' — iron and its alloys, chiefly steel — which are magnetic and prone to rusting, as opposed to 'non-ferrous' metals such as aluminium, copper, and brass. In chemistry, however, the word has a more precise meaning: it designates iron in its +2 (bivalent) oxidation state, as in ferrous oxide or ferrous sulfate, distinguishing such compounds from their 'ferric' counterparts, in which iron takes the +3 state. The word derives from the Latin ferrum, meaning iron, a root that also gives us the chemical symbol Fe. Ferrous is largely a technical term, encountered in metallurgy, recycling, medicine (notably ferrous supplements for anaemia), and chemistry, yet its basic sense — simply 'of iron' — is easy to grasp once the Latin connection is known.
Containing or relating to iron.
"The magnet attracted every ferrous object on the workbench."
(Chemistry) Of iron in the bivalent (+2) oxidation state.
"Ferrous chloride is used as a reducing agent in various industrial processes."
This sense contrasts with 'ferric' (iron +3); modern chemistry often prefers iron(II)/iron(III) notation instead.
That magnet sticking to your fridge? Thank ferrous metals — it's the chemistry of iron itself that makes magnetism possible.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of ferrous
Ferrous comes from the Latin ferrum, meaning 'iron', via the adjectival form ferreus, 'made of iron'. It entered English in the mid-seventeenth century, initially meaning simply 'of or containing iron'. The narrower chemical sense distinguishing bivalent iron (ferrous) from trivalent iron (ferric) developed later with classical nomenclature in chemistry. The same Latin root underlies related words such as ferric, farrier, and the chemical symbol for iron, Fe.
How ferrous is actually used
In everyday and industrial usage, 'ferrous' broadly means 'containing iron', especially of metals. In strict chemical nomenclature it specifically denotes iron(II), the +2 oxidation state; this older -ous/-ic naming system is increasingly replaced by Stock notation (iron(II), iron(III)) but remains common in trade and pharmacological contexts.
Easily confused with ferrous
Ferrous refers to iron in the +2 (bivalent) oxidation state, while ferric refers to iron in the +3 (trivalent) state.