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[pahy-on] /ˈpaɪ ɒn/
noun, Physics.
the first meson to be discovered: it has spin 0 and may be positively or negatively charged or neutral; charged pions decay into a muon and a neutrino or antineutrino. Symbol: π.
Also called pi meson.
Origin of pion
First recorded in 1950-55; pi (meson) + -on1 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for pion
Historical Examples
  • Do not forget next week at the home of Endora, on the Mountain of pion.

    Saronia Richard Short
  • I refer to the pion pine, of which there are several species.

    North America Israel C. Russell
  • But he turned and scrambled up a rocky bank into the pion woods that border the benches of the Meteetsee.

    The Biography of a Grizzly Ernest Seton-Thompson
  • This heres the Wagon Tire House, returned its proprietor, rising and shaking the pion slivers from her checked apron.

  • The dense forest consists of pion pine, juniper, Douglas fir, and western yellow pine.

  • This limited selection was perhaps augmented by pion nuts, yucca fruit, and other indigenous products found in abundance.

  • Outstanding was an unusual bird pendant of hematite with crystal eyes set into drilled sockets with pion gum.

  • They found Suzanne and Arabella industriously carrying in aprons full of pion chips for the kitchen stove.

    Heart's Desire

    Emerson Hough
  • By-and-by they came to a marvelous cave in the Hill of pion and entered into it and feasted, and presently they hurried on again.

    The Innocents Abroad Mark Twain (Samuel Clemens)
  • The new fronds of the pion had expanded to full size and now their needles quivered in the heat of the almost summer-like day.

    The Heart of Canyon Pass Thomas K. Holmes
British Dictionary definitions for pion


(physics) a meson having a positive or negative charge and a rest mass 273.13 times that of the electron, or no charge and a rest mass 264.14 times that of the electron
Word Origin
C20: from Greek letter pi1 + 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 pion

1951, from Greek letter pi + -on.

Online Etymology Dictionary, © 2010 Douglas Harper
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pion in Science
A meson occurring either in a neutral form with a mass 264 times that of an electron and a mean lifetime of 8.4 × 10-17 seconds or in a positively or negatively charged form with a mass 273 times that of an electron and a mean lifetime of 2.6 × 10-8 seconds. The pion was once believed to be the particle that mediates the strong force, which holds nucleons together in the nucleus; it is now believed that the gluon is the mediator particle. Pions do interact with nucleons, however, and are able to transform neutrons into protons and vice versa. Also called pi-meson. See Table at subatomic particle.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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