means A subatomic particle with no electric charge that, together with protons, makes up the nucleus of an atom.

from Coined in the 1920s from 'neutral' plus the '-on' ending that physics had adopted for its particle zoo (electron, proton). The '-on' itself drifted in from words like 'ion' — Greek for 'going' — until it simply became the suffix you slap on anything small and fundamental. So 'neutron' is, quite literally, 'the neutral one,' named for what it refuses to do: carry a charge. James Chadwick confirmed its existence experimentally in the early 1930s, but the name had been waiting in the wings before the particle was even pinned down.