- IPA: ˈn(y)o͞oträn
- (countable) A neutron is a type particle in the nucleus (center) of an atom that is the largest out of all the particles in an atom, weighs the most and has no charge. There are sometimes different numbers of them in an atom, which make isotopes (atoms that have different numbers of neutrons). They can also change the atomic mass of an atom (how much an atom weighs).
- Neutrons take up most of the space in an atom.