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Tetr- is a combining form used like a prefix meaning “four.” It is used in many scientific and other technical terms.

In chemistry, tetr- is specifically used to indicate the number of atoms or groups of atoms in compounds, e.g., tetroxide.

Tetr- ultimately comes from the Greek ��é�ٳٲ������, meaning “four.” The name of the classic video game Tetris is based in part on this Greek root. Find out the rest of the story of how Tetris got its name here.

The Latin word for “four” is quattor, source of the combining forms quadr-, quadra-, quadri-, and quadru-. Learn about their specific applications in our �y��vlogs That Use articles for the forms.

Tetr- is a variant of tetra-, which loses its -a– when combined with words or word elements beginning with vowels.

Want to know more? Read our �y��vlogs That Use tetra- article.

An example of a technical term that features tetr- is tetrarch, “any ruler of a fourth part of a region,” among other senses. So, imagine a country that was divided into four parts, each ruled by a queen; each queen would be a tetrarch of the country.

The first part of the word, tetr-, means “four.” So, what about the -arch portion of the word? It is a combining form meaning “chief, leader, ruler,” from the Greek á������Dz�. Tetrarch has a literal sense of “four rulers.”

The word tetrarch comes from the Greek �ٱ�ٰ�á������ŧ��, which uses the equivalent form of tetra- in the language.

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

• tetracid
• tetrad (using the equivalent form of tetr- in Greek)
• tetryl
• tetrode
• tetrose
• tetroxide

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

• tri-
• tetano-
• tera-
• terat-

A tetrode is a kind of vacuum tube used in electronics. Based on the meaning of tetr-, how many electrodes does a tetrode contain?