noun
Standard term for a flotation device worn on the body, used in maritime, aviation, and safety contexts. Often interchangeable with ライフジャケット.
See also: ライフジャケット
船に乗るときは救命胴衣を着用してください。
Please wear a life jacket when boarding the boat.
Common loanword synonym; 救命胴衣 is the native Japanese term and may sound slightly more formal or technical.
Compound of 救命 (life-saving) and 胴衣 (vest, jacket). The exact historical derivation is uncertain; the spelling is conventionally associated with the meaning.