n. Abbr. p
The stable, positively charged nucleon, having a mass 1,836 times that of an electron and being a baryon composed of two up quarks and one down quark. The proton is a basic component of all atomic nuclei and the nucleus of the protium isotope of hydrogen.
[From Greek prōton, neuter of prōtos, first; see per1 in the Appendix of Indo-European roots.]
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