for·tu·i·tous (fôr-tĭ-təs, -ty-)
1. Happening by accident or chance. See Synonyms at accidental.
2. Resulting in good fortune; lucky.
[Latin fortuītus; see bher-1 in the Appendix of Indo-European roots.]
Usage Note: The traditional meaning of fortuitous is "happening by chance, accidental." Perhaps because many chance events are favorable or because of the similarity of fortuitous to fortunate and felicitous, fortuitous has acquired the meaning "characterized by good fortune, lucky." (Note that the word fortunate underwent a similar shift in meaning centuries ago.) In our 2005 survey, a solid majority of the Usage Panel accepted the use of the word to mean "lucky." Some 68 percent accepted the sentence The photographer felt that it was very fortuitous that she was in place to take the winning photo, where the adverb very rules out the possibility that the word might mean "accidental." A similar percentage (67) accepted the sentence The meeting proved fortuitous: I came away with a much better idea of my role, where the verb prove makes the meaning "accidental" an unlikely fit. This two-thirds majority stands in stark contrast to the 85 percent that rejected this same sentence in 1967. Nonetheless, writers should take care to avoid creating contexts in which the meaning of the word is ambiguous.
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