Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A stable, positively charged subatomic particle in the baryon family having a mass 1,836 times that of the electron. See Table at subatomic particle.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element; the nucleus of the most common isotope of hydrogen; composed of two up quarks and a down quark

from The Century Dictionary and Cyclopedia

  • n. The first inception or rudiment of a structure or organ in the embryo: a term suggested as an equivalent of the German anlage.
  • n. A term designating certain products of tryptie digestion which are obtained from the protamins and which, supposedly, are intermediary between these and the end-products.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a stable particle with positive charge equal to the negative charge of an electron

Etymologies

From Greek prōton, neuter of prōtos, first; see per1 in Indo-European roots.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Ancient Greek πρῶτον (prōton), neuter of πρῶτος (prōtos, "first") (Wiktionary)

Examples

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