noun

• An unexpected event with negative consequences occurring without the intention of the one suffering the consequences, and (in the strict sense) not directly caused by humans.
• (transport) A collision or crash of a vehicle, aircraft, or other form of transportation that causes damage to the transportation involved; and sometimes injury or death to the transportation's occupants or bystanders in close proximity. (but see Usage notes)
  "There was a huge accident on I5 involving 15 automobiles."
• (uncountable) Chance; random chance.
  "c.1861-1863, Richard Chevenix Trench, in 1888, Letters and memorials, Volume 1, Thou cam'st not to thy place by accident, / It is the very place God meant for thee; […]"
• Any property, fact, or relation that is the result of chance or is nonessential or nonsubstantive.
  "An adjective, so called because adjectitious, or added to a substantive, denotes some quality or accident of the substantive to which it is joined […]"

adj

• (transport) Designating any form of transportation involved in an accident.
  "The NTSB report revealed that the accident airplane was a Cessna 172."