noun
bulletproof vest
A protective vest designed to stop bullets; commonly used in police, military, and security contexts.
警察官は防弾チョッキを着用していた。
The police officer was wearing a bulletproof vest.
Compound of 防弾 (bulletproof) and チョッキ (vest, from Portuguese 'jaqueta' or possibly Dutch 'jak'). The exact derivation of チョッキ is uncertain, but it is a well-established loanword in Japanese.