Meaning of ATOM in English

n.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

Oxford English vocab.      Оксфордский английский словарь.