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Ferro- is a combining form used like a prefix meaning “iron.” Ferro- is often used in scientific terms, especially in chemistry.

In many terms from chemistry, ferro- is used specifically to mean “ferrous,” a technical term meaning “of or containing iron, especially in the bivalent state,” which is when an iron ion contains two valence electrons.

Ferro- comes from Latin ferrum, meaning “iron.” The Greek equivalent was ��í��ŧ���Dz�, “iron,” which is the source of the combining form sidero-, as in siderite and siderocyte.

What are variants of ferro-?

When combined with words or word elements that begin with a vowel, ferro- becomes ferr-, as in ferrite.

The combining form ferri- shares the same Latin root as ferro-, but is used in terms from chemistry to mean “ferric,” meaning “of or containing iron, especially in the trivalent state,” which is when an iron ion contains three valence electrons.

Want to learn more? Check out our 51�Թ�s That Use entries for ferr- and ferri-.

An example of a technical term that features the form ferro- is ferrotype, also known as tintype, meaning “a positive photograph made on a sensitized sheet of enameled iron or tin.”

While ferro- means “iron,” the -type part of the word means “type, especially in names of photographic processes,” from Greek ��ý��Dz�, meaning “blow, impression.” Ferrotype therefore literally means “iron impression.”

What are some words that use the combining form ferro-?

• ferroalloy
• ferrocement
• ferrocene
• ferrocyanide
• ferroelectric
• ferromagnet
• ferronickel

What are some other forms that ferro- may be commonly confused with?

• facio-
• fascio-

Given the meaning of ferro-, what are the qualities of a ferromagnetic substance?