noun

1. a happening that is not expected, foreseen, or intended
2. an unpleasant and unintended happening, sometimes resulting from negligence, that results in injury, loss, damage, etc.
3. fortune; chance to meet by accident
4. an attribute or quality that is not essential
5. Geog., Geol. an irregular formation
6. Law an unforeseen event that occurs without anyone's fault or negligence

Etymology: ME < OFr < L accidens, prp. of accidere, to fall upon, happen < ad-, to + cadere, to fall: see case