noun
country that has suffered nuclear bombing
Refers to a nation that has experienced atomic or nuclear bomb attacks, most commonly used for Japan as the only country to have suffered atomic bombings in wartime.
日本は世界で唯一の被爆国です。
Japan is the only country in the world to have suffered atomic bombings.
被曝 refers to radiation exposure in general, not necessarily from a nuclear bomb; 被爆国 specifically refers to a country bombed with nuclear weapons.
Compound of 被爆 (hibaku, 'being bombed (nuclear/atomic)') + 国 (koku, 'country').