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.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.