1. An unpleasant, dangerous, or disastrous event or outcome that one narrowly avoids. No one was hurt in the accident, but it was a close-run thing—if the fuel tank had been hit, we all would have died. It was a close-run thing, but thankfully the emergency surgery managed to remove the cancerous tissue before it spread to other parts of my body. The last-minute deal will avert a government shutdown, but it will have been a close-run thing.

2. A very narrow margin of success or failure. After finding out I got the job, I learned from a friend within the company that it was a close-run thing due to the yearlong gap in my résumé. It was a close-run thing in the final moments of the race, but the former champion was unable to overcome the lead of his rival.