: 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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Any scenario in which scalar-nucleon particles interact strongly with protons and neutrons would have cooled these stars far more than what telescopes actually see.
—
Rupendra Brahambhatt, Interesting Engineering, 6 Dec. 2025
But when a stream of solar protons hits, radiation levels on Earth's surface and around the planet suddenly spike.
—Tereza Pultarova, Space.com, 4 Dec. 2025
Using that definition, scientists can explain basic puzzles about matter, like why protons are always paired with neutrons, and why the energy of an atom comes in discrete quantities.
—Leila Sloman, Quanta Magazine, 3 Dec. 2025
When the particles strike a proton inside the detector, a reaction triggers two light flashes that ping photomultiplier tubes and get converted into electrical signals.
—Jeanna Bryner, Scientific American, 26 Nov. 2025
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Rupendra Brahambhatt, Interesting Engineering, 6 Dec. 2025
But when a stream of solar protons hits, radiation levels on Earth's surface and around the planet suddenly spike.
—Tereza Pultarova, Space.com, 4 Dec. 2025
Using that definition, scientists can explain basic puzzles about matter, like why protons are always paired with neutrons, and why the energy of an atom comes in discrete quantities.
—Leila Sloman, Quanta Magazine, 3 Dec. 2025
When the particles strike a proton inside the detector, a reaction triggers two light flashes that ping photomultiplier tubes and get converted into electrical signals.
—Jeanna Bryner, Scientific American, 26 Nov. 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 19 Dec. 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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