FORTUITY
accident, stroke, fortuity, chance event
(noun) anything that happens suddenly or by chance without an apparent cause; “winning the lottery was a happy accident”; “the pregnancy was a stroke of bad luck”; “it was due to an accident or fortuity”
Source: WordNet® 3.1
Noun
fortuity (countable and uncountable, plural fortuities)
(uncountable) The state of being fortuitous.
(countable) A fortuitous event; an accident.
Source: Wiktionary
For*tu"i*ty, n. Etym: [Cf. F. fortuité.]
Definition: Accident; chance; casualty. D. Forbes (1750).
Source: Webster’s Unabridged Dictionary 1913 Edition