means A calm, balanced self-possession — the ability to stay steady, graceful, and composed under pressure.

from From Old French 'pois' meaning weight, from Latin 'pensum,' the amount weighed out, ultimately from 'pendere,' to weigh or hang. The same scale-and-balance image that gives us 'pension' and 'pensive' gives us poise: originally it meant literal heaviness or equilibrium, and only later did English tip the meaning toward the inner sort of balance — holding yourself level the way a steady scale holds two pans even.