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[proh-ton] /ˈproʊ tɒn/
noun, Physics, Chemistry
a positively charged elementary particle that is a fundamental constituent of all atomic nuclei. It is the lightest and most stable baryon, having a charge equal in magnitude to that of the electron, a spin of ½, and a mass of 1.673 × 10− 27 kg. Symbol: P.
1915-20; noun use of Greek prôton, neuter of prôtos first
Related forms
protonic, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for proton
  • The pull appeared as strong as an electron toward a proton.
  • Because the quarks and gluons within a proton are constantly interacting, a proton-proton collision is an inherently messy affair.
  • For example, a proton has a positive electric charge, but an antiproton has a negative electric charge.
  • The molecules are composed of atoms, which in turn are composed of electrons and clusters of proton particles.
  • Thus, people with comparatively lesser neutrons in their body composition exhibit the effect of dominant proton.
  • proton-pump or acid-pump inhibitors are probably the best drug treatments for reflux symptoms related to scleroderma.
  • It is usually combined with medications, such as epinephrine and intravenous proton pump inhibitors.
  • proton therapy is another kind of radiation used to treat prostate cancer.
  • Long-term use of proton-pump inhibitors may reduce the duration of treatments.
  • The researchers think these may be able to work as proton-exchange membranes in their own right.
British Dictionary definitions for proton


a stable, positively charged elementary particle, found in atomic nuclei in numbers equal to the atomic number of the element. It is a baryon with a charge of 1.602176462 × 10–19 coulomb, a rest mass of 1.672 62159 × 10–27 kilogram, and spin 1/2
Word Origin
C20: from Greek prōtos first
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 proton

1920 in physics, coined by English physicist Ernest Rutherford (1871-1937) from noun use of Greek proton, neuter of protos "first" (see proto-), on analogy of electron; supposedly because hydrogen was hypothesized as a constituent of all the elements. The word was used earlier in embryology (1893) as a translation of German anlage ("fundamental thing") based on Aristotle's phrase he prote ousia to proton.

Online Etymology Dictionary, © 2010 Douglas Harper
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proton in Medicine

proton pro·ton (prō'tŏn')
A stable, positively charged subatomic particle in the baryon family having a mass 1,836 times that of the electron.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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proton in Science
A stable subatomic particle in the baryon family having a mass of 1.672 × 10-24 grams (1,836 times that of the electron) and a positive electric charge of approximately 1.602 × 10-19 coulombs. Protons make up part of the nucleus of all atoms except hydrogen, whose nucleus consists of a single proton. In neutral atoms, the number of protons is the same as the number of electrons. In positively charged atoms, the number of protons is greater than the number of electrons, and in negatively charged atoms electrons outnumber protons. Protons are believed to be composed of two up quarks and one down quark. See Table at subatomic particle.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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proton in Culture
proton [(proh-ton)]

An elementary particle with a positive charge, found in the nucleus of an atom.

Note: A proton is over a thousand times heavier than an electron.
Note: Protons and neutrons make up most of an atom's mass.
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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proton in Technology

1. A home computer made by Acorn Computers under a contract won from the BBC in April 1981.
2. Something to do with Microsoft SoftLib?
The Free On-line Dictionary of Computing, © Denis Howe 2010
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