Select the most suitable antonym from the given choices for the word: Sangfroid

'Sangfroid' is a word of French origin (literally 'cold blood') meaning composure, self-possession and coolness of mind, especially the ability to stay calm and unflustered under strain or danger.

An antonym must express the opposite idea, i.e. agitation or loss of calm. Among the choices, 'Equanimity', 'Steadiness' and 'Aplomb' all describe calmness, poise or composure, so they are synonyms of the cue word, not antonyms. 'Turbulence' denotes agitation, disturbance and unrest, which is the direct opposite of calm composure.

Hence the most suitable antonym is 'Turbulence'.