An accident is an unintended event, often (but not always) with harmful results. The opposite of an accident is a planned, deliberate act.
With respect to transport, an accident is a collision between a vehicle and a person or another vehicle. About 48,000 Americans are killed each year in car accidents. Air travel is much safer, with only about a hundred fatalities per year on average (most years there are no airliner crashes).
Accidents and the religious life
We can't pray ... "Please God, prevent an accident from happening to me." Rather pray "Please lead me in your will." We do have accidents. Maybe that's His will, and as a result of that we gain a different level, a higher level. We are bound to get to a higher level if our mind is basically good. Who knows what will happen in the future? If something happens, everyone may agree it is a tragedy. But there are two ways for us: either complain, or continue on contemplating what chance this offers me. Who is the wise person, the sagacious person? The wise person does not complain. - Rev. Sun Myung Moon, In Yun and Encounter