of, pertaining to, resulting from, or using atoms, atomic energy, or atomic bombs

an atomic explosion.

propelled or driven by atomic energy

an atomic submarine.

Chemistry . existing as free, uncombined atoms.

extremely minute.

adjective

diminutive , fragmentary , granular , microscopic , minute , atom-powered , fissionable , thermonuclear , energy , fission , infinitesimal , molecular , submarine , tiny