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a combining form meaning “swift,” used in the formation of compound words: tachygraphy.
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Compare tacho-.

Origin of tachy-

<Greek, combining form of tachýs
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021


What does tachy- mean?

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 tachýs, 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 Words That Use tacho- article.

Examples of tachy-

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 Words 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-?

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

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.

Break it down!

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

British Dictionary definitions for tachy-



combining form
swift or acceleratedtachycardia; tachygraphy; tachylyte; tachyon; tachyphylaxis

Word Origin for tachy-

from Greek takhus swift
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for tachy-


Rapid; accelerated:tachycardia.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.