1. An unexpected usually sudden event that occurs without intent or volition although sometimes through carelessness, unawareness, ignorance, or a combination of causes and which produces an unfortunate result (as an injury) for which the affected party may be entitled to relief under the law or to compensation under an insurance policy: "The accidental collision between the two cars was being investigated by the police."
2. Happening by chance; belonging but not essential; unplanned, unintentional, unpremeditated, uncalculated; unexpected, fortuitous; chance, random: "The meeting of Dale and Mike on the street was purely accidental."