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Tachy- is a combining form used like a prefix meaning “swift.” It is often used in scientific and medical terms.

Tachy- comes from the Greek �ٲ�����ý��, meaning “swift.”

What are variants of tachy-?

A variant of tachy- is tacheo-, as in tacheometer. Closely related to tachy- is the combining form tacho-, which you can learn more about in our 51�Թ�s That Use tacho- article.

An example of a medical term that features the combining form tachy- is tachypnea, meaning “excessively rapid respiration.”

The word tachypnea is made of two combining forms. The first is tachy- which we know means “swift.” The second is -pnea which means “breath, respiration,” as we explain in our 51�Թ�s That Use -pnea article. Tachypnea translates literally to “swift breathing.”

Some theoretical physicists have speculated on the existence of the tachyon, a theoretical subatomic particle that travels faster than the speed of light—which would violate the laws of physics as we know them!

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

• tachycardia
• tachygraphy
• tachylyte
• tachymeter
• tachyon
• tachyrhythmia
• tachytelic

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

• pachy-
• techno-

Despite being a homonym, the word tacky does not share the same root as tachy-. Find out what makes tacky unique at our entry for the word.

Tachy- means “swift” and -cardia refers to the heart. Can you figure out, then, what tachycardia is?