- Of or relating to particles that are smaller than an atom.
- Having dimensions or participating in reactions characteristic of the constituents of the atom.
- (physics) Relating to particles that are constituents of the atom, or are smaller than an atom; such as proton, neutron, electron, etc.
- Relating to any length or mass that is smaller in scale than a the diameter of a hydrogen atom.
- The electron microscope is able to resolve detail at the subatomic level.