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

In chemistry, tetra- is specifically used to indicate four atoms or four groups of atoms in compounds, e.g., tetrachloride.

Tetra- 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.

What are variants of tetra-?

When combined with words or word elements that begin with a vowel, tetra- becomes tetr-, as in tetracid.

One example of a word you may have encountered that features tetra- ������tetragon, “a polygon having four angles or sides,” such as a square or rectangle. A tetragon is also known as a quadrangle or quadrilateral.

The first part of the word, tetra-, means “four,” as we know. The -gon portion of the word may also look familiar: it is a combining form meaning “angled” or “angular,” from the Greek ��ō��í��. Tetragon literally translates to “four-angled.”

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

Another geometric shape using the combining form tetra- is tetrahedron, a triangular pyramid; it’s so named because the shape is formed using four (tetra-) faces (-hedron).

You may have also heard of a tetralogy, which refers to a series of four related plays, novels, films, video games, or other media. It’s like a trilogy—plus one. Shakespeare’s so-called Henriad is an example of a tetralogy. It consists of four connected history plays: Richard II, Henry IV, Part 1, Henry IV, Part 2, and Henry V.

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

Many of the following words use the equivalent form of tetra- in Greek.��

• tetrabasic
• tetrabrach
• tetracycline
• tetradactyl
• tetrafluoroethylene
• tetragram
• Tetragrammaton
• tetrameter
• tetrapod
• tetrasaccharide
• tetraspore

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

• tri-
• tetano-
• tera-
• terato-

The combining form -dactyl means “possessing fingers or toes” of the kind specified by the first part of the word. A tetradactyl is an animal with how many toes?