atomic bomb; A-bomb
Formal term for a nuclear fission weapon. In everyday Japanese, the abbreviation 原爆 is more common, but 原子爆弾 is used in formal, historical, or technical contexts.
See also: 原爆
An atomic bomb was dropped on Hiroshima.
原子爆弾の開発は世界の歴史を変えた。
The development of the atomic bomb changed world history.