best man; groomsman; bridesmaid
Refers to a person who assists the bride or groom at a wedding ceremony. Can be used for either gender, though context often clarifies.
He served as his friend's best man at the wedding.
花嫁の介添人は美しいドレスを着ていた。
The bride's bridesmaid wore a beautiful dress.
Historical term for a person who assists a duelist, ensuring fair play and acting as a witness. Rare in modern usage outside historical contexts.
決闘の際、介添人は武器を確認する役目があった。
In a duel, the second had the role of checking the weapons.