As Evan Jenkins wrote here in 1997, “fortuitous,” strictly speaking, does not mean “lucky”; it means “by chance.” So when a snake bites a mouse that just happened to be in its path, it is “fortuitous”—lucky for the snake, not so much for the mouse. Just an accident of timing.
But, possibly because “fortuitous” begins the same way as “fortunate” and “fortune,” in the past 100 years or so, “fortuitous” has also come to mean, as Webster’s New World College Dictionary has it, “bringing, or happening by, good luck; fortunate.” (Emphasis added.) These days, nearly every usage of “fortuitous” in U.S. media is the “lucky” one.
The venerable Oxford English Dictionary has but one definition of “fortuitous”: “That happens or is produced by fortune or chance; accidental, casual.” That’s the only definition accepted by what Bryan A. Garner calls “die-hard snoots.” One of those is The New York Times, whose stylebook says that “fortuitous means happening by chance. It does not mean fortunate.” Another is Garner himself; his Modern American Usage calls using “fortuitous” to mean “fortunate” “a very unfortunate thing.” That “unfortunate” usage is at Stage 3 on his five-stage Language-Change Index, meaning “still avoided in careful usage.”
Now comes the Fifth Edition of the American Heritage Dictionary of the English Language, whose second definition of “fortuitous” is “Resulting in good fortune; lucky.” Its usage panel did an about-face in the past 40 years; in 1967, 85 percent of the panel rejected the usage of “fortuitous” in this passage: “The meeting proved fortuitous: I came away with a much better idea of my role.” In 2005, 67 percent accepted it. “Nonetheless,” that dictionary says, “writers should take care to avoid creating contexts in which the meaning of the word is ambiguous.”
Such a sentence might be “It was fortuitous that the final exam, which had no make-ups, fell on the one day I was sick.” On the one hand, the student was lucky to not have to take the exam. On the other hand, without make-ups, that student probably flunked. Not so lucky. Which was meant?
If you want to be absolutely clear that something happened by chance and was good luck, “serendipity” is unambiguous. It means “a seeming gift for finding something good accidentally” or “luck, or good fortune, in finding something good accidentally.” “Serendip” is an old Persian name for Sri Lanka, itself a new name for Ceylon. The OED says the word “serendipity” was coined in 1754 by Horace Walpole, who wrote to Horace Mann that he “had formed it upon the title of the fairy-tale ‘The Three Princes of Serendip,’ the heroes of which ‘were always making discoveries, by accidents and sagacity, of things they were not in quest of.’” (Note that even in 1754, learned men were ending sentences in prepositions, but that’s another column )
Remember, too, that there is “good luck” and “bad luck,” so you or your context must make clear which it is. “Lucky,” though, always means good luck, since “unlucky” is just as handy.
Similarly, “fortune” needs help; it means simply “luck, chance, fate.” A qualifier or context is needed to give “fortune” value. “She had the good fortune ,” “He had the misfortune ,” “They made a fortune in the market ” “Fortunate” is unambiguously good, like “lucky.”
So it turns out that “fortune” and “fortuitous” really do have a lot in common. As W.C. Fields would say, “How fortuitous!”