noun
parcel bomb; mail bomb; letter bomb
A bomb disguised as or hidden inside a parcel, package, or letter, sent through the mail or a delivery service.
郵便局で小包爆弾が見つかった。
A parcel bomb was found at the post office.
Compound of 小包 (こづつみ, 'parcel') and 爆弾 (ばくだん, 'bomb').