ac·ci·dent 
(ăksĭ-dənt, -dĕnt′)
(ăksĭ-dənt, -dĕnt′)n.
1.
a. An unexpected and undesirable event, especially one resulting in damage or harm: an accident on the assembly line; car accidents on icy roads.
b. An unforeseen event that is not the result of intention or has no apparent cause: A series of happy accidents led to his promotion.
c. An instance of involuntary urination or defecation.
2. Lack of intention; chance: ran into an old friend by accident.
3. Philosophy An attribute of a substance that is not essential to its nature.
[Middle English, chance event, from Old French, from Latin accidēns, accident-, present participle of accidere, to happen : ad-, ad- + cadere, to fall; see kad- in the Appendix of Indo-European roots.]