an unfortunate incident that happens unexpectedly and unintentionally, typically resulting in damage or injury

he had an accident at the factory

if you are unable to work owing to accident or sickness

an event that happens by chance or that is without apparent or deliberate cause

the pregnancy was an accident

it is no accident that Manchester has produced more than its fair share of professional comics

(in Aristotelian thought) a property of a thing which is not essential to its nature