Definition of neutron in English:



  • A subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen.

    • ‘The mass number gives you the total number of protons and neutrons in the nucleus of that element.’
    • ‘The result would be a star made entirely of neutrons, and these could be packed together as closely as the protons and neutrons in an atomic nucleus.’
    • ‘An alpha particle consists of two protons and two neutrons; it is the nucleus of a helium atom.’
    • ‘Even the protons and neutrons in the atomic nucleus are believed to made of even smaller particles called quarks.’
    • ‘If conditions are right, protons and electrons then fuse into neutrons, creating a neutron star.’


Early 20th century: from neutral + -on.