1 a the smallest particle of a chemical element that can take part in a chemical reaction. b this particle as a source of nuclear energy.
2 (usu. with neg.) the least portion of a thing or quality (not an atom of pity).
Phrases and idioms:
atom bomb a bomb involving the release of energy by nuclear fission = fission bomb. atom-smasher colloq. = ACCELERATOR 2.
Etymology: ME f. OF atome f. L atomus f. Gk atomos indivisible
Useful english dictionary. 2012.