fortuitous
adjective (formal)

- happening by chance; coincidental, accidental

- (of something that is to your advantage) not planned, happening by chance

- fortunate, lucky

Wiktionary, Cambridge Dictionary, Merriam-Webster

NOTE: 
Fortuitous means coincidental or unplanned and does not always mean fortunate. Strictly speaking a “fortuitous” event can be either good or bad,… whereas a “fortunate” one is always good. 

Examples:
- “Running into my old friend was fortuitous.”
- “It was fortunate that I had a good amount of savings after losing my job.”

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WORD ORIGIN

The English word fortuitous comes from the Latin fortuitus, which meant “happening by chance, accidental.” This in turn comes from forte (“by chance”), which goes back to the Latin noun fors (“chance, luck”).

For its first 250 years in English (up until the early 20th century), fortuitous had only one meaning: “something that happens by chance, without being planned.” It did NOT mean “fortunate” or “lucky.”

Because fortuitous sounds very much like fortunate, many people gradually began to use it with the meaning “lucky, fortunate.” This created confusion, since “chance” and “luck” are related but not identical ideas.

Today, most English speakers use fortuitous in both ways: either “by chance” or “lucky.” Strict language purists still prefer the older, original meaning: “happening by chance, unplanned.”

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SYNONYMS

- Accidental: Happened by pure chance, not planned or intended

   "Any resemblance to actual persons is entirely accidental.” (zufällig, unbeabsichtigt)

- Fortuitous: Happened by chance, often surprisingly positive, no clear cause

   “A series of fortuitous events led to him finding his lost sister.” (zufällig, glücklicher Zufall)

- Casual: Happened without planning, intention, or seriousness

   “Train journeys and supermarket queues invite casual encounters with strangers.” (beiläufig, ungezwungen, zufällig)

- Contingent: Depends on other things happening first, uncertain

   “Our picnic happening at the weekend will be contingent upon good weather.” (abhängig von, bedingt durch, unsicher)

- Lucky: A good outcome that comes by chance rather than effort

   “He was lucky to catch the last train home.” (Glück haben)

- Fortunate: Similar to lucky, but more formal; often implies gratitude for a good outcome

   “We are fortunate to have such supportive friends.” (glücklich, vom Schicksal begünstigt)

- Serendipitous: A happy accident: finding something good without looking for it

   “It was a serendipitous discovery that changed the course of medicine.” (glücklicher Zufall, Entdeckung)

- Unforeseen: Not expected or planned, can be good or bad

   “The project faced several unforeseen delays.” (unvorhergesehen)

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SMUGGLE
 OWAD into a conversation today, say something like:

“Even most native English speakers do not understand the difference between ‘FORTUITOUS’ and ‘fortunate’. "

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P L E A S E   S U P P O R T   O W A D