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[tak-ee-on] /ˈtæk iˌɒn/
noun, Physics.
a hypothetical particle that travels faster than the speed of light.
Origin of tachyon
First recorded in 1967; tachy- + -on1 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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British Dictionary definitions for tachyon


(physics) a hypothetical elementary particle capable of travelling faster than the velocity of light
Word Origin
C20: from tachy- + -on
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
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Word Origin and History for tachyon

1967, hypothetical faster-than-light particle, from tachy- "swift" + -on.

Online Etymology Dictionary, © 2010 Douglas Harper
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tachyon in Science
A hypothetical subatomic particle that travels faster than the speed of light. Although the principles of relativity forbid the acceleration of a particle past the speed of light, they do not prohibit the existence of particles that have always moved faster than that speed. No such particle has ever been detected.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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