- If something happens out of the blue, it happens very unexpectedly without warning or preparation.
- An event that happens from an unexpected or unforeseen source.
- Suddenly and unexpectedly.
1. I was worried about being unemployed when out of the blue, I was offered a job.
2. I hate it when out of the blue things start going wrong.
3. Out of the blue, my boyfriend surprised me with a gift!
4. They organised a party to celebrate out of the blue.
no predicted, surprising, unanticipated, unexpected, unforeseen, unplanned, unprepared for