Merriam-Webster Collegiate Dictionary - accident

 noun  Etymology: Middle English, from Middle French, from Latin ~-, accidens nonessential quality, chance, from present participle of accidere to happen, from ad- + cadere to fall — more at chance  Date: 14th century  1.  a. an unforeseen and unplanned event or circumstance  b. lack of intention or necessity ; chance met by ~ rather than by design  2.  a. an unfortunate event resulting especially from carelessness or ignorance  b. an unexpected and medically important bodily event especially when injurious a cerebrovascular ~  c. an unexpected happening causing loss or injury which is not due to any fault or misconduct on the part of the person injured but for which legal relief may be sought  d. — used euphemistically to refer to an involuntary act or instance of urination or defecation  3. a nonessential property or quality of an entity or circumstance the ~ of nationality