Quick answer
Fortuitous strictly means happening by chance — with no implication that the chance was good. Fortunate means lucky. A fortuitous meeting is an accidental one; a fortunate one is a welcome one. In practice fortuitous is now widely used to mean "luckily accidental", which blurs the two.
The core difference
One word names chance; the other names good luck.
- fortuitous — by chance, accidental: a fortuitous encounter.
- fortunate — lucky, favourable: fortunate timing.
The drift
Fortuitous has absorbed a sense of good luck through its resemblance to fortunate, and dictionaries now record that meaning. Purists object, but the drift is well advanced. The practical consequence is that fortuitous alone no longer reliably signals neutrality about the outcome.
If you need the neutral word
Write accidental, chance or coincidental. Those cannot be misread as implying the outcome was welcome.
Frequently asked questions
Does fortuitous mean lucky?
Strictly it means by chance, with no implication about the outcome — though the lucky sense is now widely used and recorded.
What should I write for pure chance?
Accidental, chance or coincidental — none of which can be read as implying good luck.
Are the words related?
Both come from Latin fortuna, chance or fortune, which is why the senses have converged.
