Definition: Composure or coolness shown in danger or under trying circumstances. Sometimes spelled ‘sang-froid’.
In French, it literally means ‘cold blood’—English borrowed the word in the 18th century.
I think I first read this word in The Three Musketeers—about a 4th musketeer who enjoyed fighting duels (no doubt with a lot of sangfroid) and falling in love.
That book was translated in 1846—but by then, English already had ‘sangfroid’ for 100 years …