- noun a particle with a positive charge and with mass almost identical to that of a neutron, found in the nucleus of an atom
- Positively-charged particle with mass almost identical to that of the neutron, and found with neutrons in the nuclei of atoms
- (written as Proton)Russian (and former Soviet) rocket launcher used extensively in manned and unmanned spaceflight The name was also used in the 1960s for a series of Soviet satellites used to investigate cosmic rays
- A positively charged extremely stable subatomic particle which is present in all atomic nuclei. Its mass is about 1,840 times that of an electron, and slightly less than that of a neutron. A protium nucleus consists of a single proton. It is the lightest baryon, and its antiparticle is the antiproton. The number of protons in a nucleus is what differentiates all chemical elements. Protons are used, for instance, in particle accelerators.
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