means a piece of bad luck or an unfortunate event, especially one that brings real harm or hardship.

from From the prefix 'mis-' (wrong, bad — the same Germanic 'mis-' that sours 'mistake' and 'misdeed') bolted onto 'fortune,' which sailed in through French from Latin 'fortuna,' the goddess and her famous wheel of luck. So 'misfortune' is literally luck gone wrong — Fortune turning her wheel the way you'd rather she didn't.