Fortuitous

fortuitous \for-TOO-uh-tus\ adjective
1 : occurring by chance
2 : fortunate, lucky
*3 : coming or happening by a lucky chance

Example sentence:
How fortuitous it was that the day before the rattlesnake bit little Jessica, her Dad had completed a first aid course!

Did you know?
For some 250 years, until the early part of the 20th century, "fortuitous" meant one thing only: "happening by chance." This was no accident; its Latin forebear, "fortuitus," derives from the same ancient root as the Latin word for "chance," which is "fors." But the fact that "fortuitous" sounds like a blend of "fortunate" and "felicitous" (meaning "happily suited to an occasion") may have been what ultimately led to a second meaning: "fortunate." That use has been disparaged by critics, but it is now well established. Perhaps the seeds of the newer sense were planted by earlier writers applying overtones of good fortune to something that is a chance occurrence. In fact, today we quite often apply "fortuitous" to something that is a chance occurrence but has a favorable result.

*Indicates the sense illustrated in the example sentence.