bain-marie (n.)

"shallow, flat vessel containing hot water in which another vessel is placed to heat its contents gently," 1822, from French bain-marie, from Medieval Latin balneum Mariae, literally "bath of Mary." According to French sources, perhaps so called for the gentleness of its heating. Middle English had balne of mary (late 15c.). French bain was used by itself in English in various sense 15c.-17c.; it is from baigner "to bathe" (12c.), from Latin balneare, from balneum "bath" (see balneal).