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[foh-ton] /ˈfoʊ tɒn/
a quantum of electromagnetic radiation, usually considered as an elementary particle that is its own antiparticle and that has zero rest mass and charge and a spin of one. Symbol: γ.
Also called light quantum.
Origin of photon
First recorded in 1900-05; phot- + -on1 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for photon
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Historical Examples
  • Or there may be an inelastic collision, when the photon hits an atom and knocks out an electron—the old photoelectric effect.

    The Mercenaries Henry Beam Piper
  • "Well, you know what happens when a photon comes in contact with the atomic structure of matter," Kato said.

    The Mercenaries Henry Beam Piper
  • Or, the photon may be retained for a while and emitted again relatively unchanged—the effect observed in luminous paint.

    The Mercenaries Henry Beam Piper
  • There were hundreds of scintillations, each caused by a nuclear particle or photon striking the screen.

    The Blue Ghost Mystery Harold Leland Goodwin
British Dictionary definitions for photon


a quantum of electromagnetic radiation, regarded as a particle with zero rest mass and charge, unit spin, and energy equal to the product of the frequency of the radiation and the Planck constant
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 photon

"unit of electromagnetic radiation," 1926 in modern sense, from photo- "light" + -on "unit."

Online Etymology Dictionary, © 2010 Douglas Harper
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photon in Medicine

photon pho·ton (fō'tŏn')
The quantum of electromagnetic energy, generally regarded as a discrete particle having zero mass, no electric charge, and an indefinitely long lifetime.

pho·ton'ic adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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photon in Science
The subatomic particle that carries the electromagnetic force and is the quantum of electromagnetic radiation. The photon has a rest mass of zero, but has measurable momentum, exhibits deflection by a gravitational field, and can exert a force. It has no electric charge, has an indefinitely long lifetime, and is its own antiparticle. See Note at electromagnetic radiation. See Table at subatomic particle.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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photon in Culture
photon [(foh-ton)]

The quantum, or bundle of energy, in which light and other forms of electromagnetic radiation are emitted. (See atom.)

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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