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axion

American

[ak-see-on] / ˈæk siˌɒn /

noun

Physics.

a hypothetical particle having no charge, zero spin, and small mass: postulated in some forms of quantum chromodynamics.

axion British

/ ˈæksɪˌon /

noun

physics a hypothetical neutral elementary particle postulated to account for certain conservation laws in the strong interaction

"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

Etymology

Origin of axion

1978; perhaps axi(al current) + -on ¹

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

In solving this puzzle, the PQ symmetry introduces the axion, a hypothetical particle that is a leading candidate for dark matter.

From Science Daily • Dec. 7, 2025

The models in our paper are based on a different, ultra-light version of the axion that would act as dark energy, not dark matter.

From Science Daily • Nov. 4, 2025

“If dark matter were a QCD axion, it would essentially be invisible to us,” O’Hare told Salon in a video call.

From Salon • Dec. 26, 2024

"It seems almost impossible to have a consistent theory of gravity combined with quantum mechanics that does not have particles like the axion," Safdi said.

From Science Daily • Nov. 21, 2024

A few have also pursued the axion, a nearly massless particle originally proposed to solve a different problem with the theory of the strong nuclear force.

From Science Magazine • Nov. 20, 2024

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023