: 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
Examples of proton in a Sentence
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The result is that all the protons and electrons in the star are crushed into neutrons, and the mass of the incredibly dense object remains comparable to the sun, but the size is comparable to a city, as explained by NASA.
—
Adam Harrington, CBS News, 9 Feb. 2026
Matter’s more ordinary building blocks, protons and neutrons, settled out of it as the universe expanded and cooled, and the strange stuff vanished, never to be seen again.
—Joseph Howlett, Scientific American, 6 Feb. 2026
Lambdas are ideal for spin research because the direction of a lambda’s spin can be inferred from the direction in which a proton or antiproton is emitted during its decay.
—Georgina Jedikovska, Interesting Engineering, 5 Feb. 2026
Baptist’s plans in Palm Beach County include continuing to expand by adding to its existing hospitals, building a new proton therapy center for cancer patients at Boca Regional Hospital, expanding outpatient services in Wellington, and adding beds at its Bethesda West hospital.
—Cindy Krischer Goodman, Miami Herald, 2 Feb. 2026
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Adam Harrington, CBS News, 9 Feb. 2026
Matter’s more ordinary building blocks, protons and neutrons, settled out of it as the universe expanded and cooled, and the strange stuff vanished, never to be seen again.
—Joseph Howlett, Scientific American, 6 Feb. 2026
Lambdas are ideal for spin research because the direction of a lambda’s spin can be inferred from the direction in which a proton or antiproton is emitted during its decay.
—Georgina Jedikovska, Interesting Engineering, 5 Feb. 2026
Baptist’s plans in Palm Beach County include continuing to expand by adding to its existing hospitals, building a new proton therapy center for cancer patients at Boca Regional Hospital, expanding outpatient services in Wellington, and adding beds at its Bethesda West hospital.
—Cindy Krischer Goodman, Miami Herald, 2 Feb. 2026
See All Example Sentences for proton
Cite this Entry
“Proton.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/proton. Accessed 13 Feb. 2026.
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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