: an elementary particle that is identical with the nucleus of the hydrogen atom, that along with the neutron is a constituent of all other atomic nuclei, that carries a positive charge numerically equal to the charge of an electron, and that has a mass of 1.673 × 10−27 kilogram
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For instance, experiments have shown the proton to be so stable that its half-life must be at least a hundred trillion trillion times the age of the universe.
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Lyndie Chiou, Scientific American, 30 Apr. 2025
This is possible because neutrons and protons are made of even smaller particles, called quarks.
—Paul Sutter, Space.com, 28 Apr. 2025
While protons are trapped in the jet by its strong magnetic fields, chargeless neutrons can get forced out of the jet into the surrounding hot cocoon of material.
—Mohammed Soliman, MSNBC Newsweek, 28 Apr. 2025
Electrons, protons and their constituent quarks… photons.
—Steven Strogatz, Quanta Magazine, 17 Apr. 2025
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Lyndie Chiou, Scientific American, 30 Apr. 2025
This is possible because neutrons and protons are made of even smaller particles, called quarks.
—Paul Sutter, Space.com, 28 Apr. 2025
While protons are trapped in the jet by its strong magnetic fields, chargeless neutrons can get forced out of the jet into the surrounding hot cocoon of material.
—Mohammed Soliman, MSNBC Newsweek, 28 Apr. 2025
Electrons, protons and their constituent quarks… photons.
—Steven Strogatz, Quanta Magazine, 17 Apr. 2025
See All Example Sentences for proton
Cite this Entry
“Proton.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/proton. Accessed 5 May. 2025.
Copy CitationKids Definition
proton
noun
pro·ton
ˈprō-ˌtän 
: an atomic particle that occurs in the nucleus of every atom and carries a positive charge equal in size to the negative charge of an electron
Medical Definition
proton
noun
pro·ton
ˈprō-ˌtän
: an elementary particle that is identical with the nucleus of the hydrogen atom, that along with neutrons is a constituent of all other atomic nuclei, that carries a positive charge numerically equal to the charge of an electron, and that has a mass of 1.673×10−24 gram
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