Translation

偶然の / 偶然起こった / 思いがけない

Meaning

Fortuitous means happening by chance rather than by plan. It often describes a lucky accident, but the core meaning is accidental, not simply good. The learner trap is using fortuitous as a fancy synonym for fortunate when no chance element is involved.

Examples

• 駅での偶然の出会いが共同研究につながりました。
  A fortuitous meeting at the station led to a joint research project.
• その発見は計画された実験ではなく、偶然の結果でした。
  The discovery was fortuitous, not the result of a planned experiment.