Adjective 1. of or relating to constituents of the atom or forces within the atom; "subatomic particles"; "harnessing subatomic energy" (pertainym) atom 2. of dimensions smaller than atomic dimensions (similar) microscopic, microscopical, small
Subatomic Definition from Encyclopedia Dictionaries & Glossaries
In the physical sciences, subatomic particles are particles much smaller than atoms. There are two types of subatomic particles: elementary particles, which according to current theories are not made of other particles; and composite particles. Particle physics and nuclear physics study these particles and how they interact.