Fortuitous (adjective)

1. Happening by chance; accidental or unexpected.
2. Lucky or advantageous, especially by chance.

Origin:

Late middle english: from latin fortuitus "happening by chance", from fortuis "by chance".

Examples:

1. It was a fortuitous meeting that brought the two scientists together.
2. The discovery of oil was a fortuitous event that changed the country's economy.
3. The fortuitous arrival of the ship saved the crew from certain death.
4. The fortuitous circumstances led to a successful outcome.
5. It was a fortuitous coincidence that they were in the right place at the right time.