means A small, usually harmless accident or piece of bad luck.

from A blend of 'mis-' — the Old English prefix meaning 'wrong' or 'badly,' the same gloomy little tag that sours 'mistake' and 'misfortune' — bolted onto the Middle English 'hap,' meaning luck or chance (from Old Norse 'happ'). So a mishap is literally 'bad luck,' and 'hap' is the same root that gives us 'happen,' 'happy,' and 'perhaps' — all of them, at heart, about whatever chance throws your way.